Open all links in a new tab (#268)

The app is usually accessed via an iframe. If you click links currently,
the new page is in the iframe itself. This is really confusing. We could
use `target=_top` to replace the current page, but Tony has said in the
past that we should go to a new tab.

We now consistently use the up-right arrow icon with every external link
to make more explicit that the links go to a new tab.

<img width="792" alt="Screenshot 2024-08-02 at 8 50 24 AM"
src="https://github.com/user-attachments/assets/7640e41b-b4f3-4519-9d60-34a7e8f730f9">

index.html

@@ -140,6 +140,7 @@ <h3 id="about-popup-links-heading">Relevant links</h3>
             <a
               class="external-link"
               href="https://parkingreform.org/resources/parking-lot-map/"
+              target="_blank"
               >Methodology and key takeaways
               <i aria-hidden="true" class="fa-solid fa-arrow-right"></i
             ></a>
@@ -148,12 +149,16 @@ <h3 id="about-popup-links-heading">Relevant links</h3>
             <a
               class="external-link"
               href="https://parkingreform.org/resources/mandates-map"
+              target="_blank"
               >PRN's Parking Mandates Map
               <i aria-hidden="true" class="fa-solid fa-arrow-right"></i
             ></a>
           </li>
           <li>
-            <a class="external-link" href="https://parkingreform.org/support/"
+            <a
+              class="external-link"
+              href="https://parkingreform.org/support/"
+              target="_blank"
               >Support this project with a donation
               <i aria-hidden="true" class="fa-solid fa-arrow-right"></i
             ></a>
@@ -207,8 +212,11 @@ <h3>FAQ</h3>
           <p>
             For details on each city boundary,
             <a
+              class="external-link"
               href="https://parkingreform.org/resources/parking-lot-map/parking-lot-map-boundary-methodology/"
-              >see this detailed methodology</a
+              target="_blank"
+              >see this detailed methodology
+              <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
             >.
           </p>
         </dd>
@@ -222,8 +230,11 @@ <h3>FAQ</h3>
             First, find how to embed iframes with your website provider. For
             example, Wordpress sites should use a
             <a
+              class="external-link"
               href="https://wordpress.com/support/wordpress-editor/blocks/custom-html-block/"
-              >Custom HTML code block</a
+              target="_blank"
+              >Custom HTML code block
+              <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
             >. Try searching for the name of your website provider and 'iframe',
             like 'Squarespace iframe'.
           </p>
@@ -250,29 +261,102 @@ <h3>FAQ</h3>
       <h3>Acknowledgments</h3>
       <p>
         This map was developed by
-        <a href="https://www.linkedin.com/in/thomas-carpenito/"
-          >Thomas Carpenito</a
-        >
+        <a
+          class="external-link"
+          href="https://www.linkedin.com/in/thomas-carpenito/"
+          target="_blank"
+          >Thomas Carpenito
+          <i aria-hidden="true" class="fa-solid fa-arrow-right"></i
+        ></a>
         with the assistance of
-        <a href="https://www.linkedin.com/in/arellanoeric/">Eric Arellano</a>,
-        <a href="https://www.linkedin.com/in/tung-lin-bb1745163/">Tung Lin</a>,
-        <a href="https://www.geocadder.bg/en/">Geocadder</a>,
-        <a href="https://www.linkedin.com/in/davidrhunt/">David Hunt</a>,
-        <a href="https://www.linkedin.com/in/ellen-schwartz-614847132/"
-          >Ellen Schwartz</a
+        <a
+          class="external-link"
+          href="https://www.linkedin.com/in/arellanoeric/"
+          target="_blank"
+          >Eric Arellano
+          <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
         >,
-        <a href="https://www.linkedin.com/in/tony-jordan-pdx/">Tony Jordan</a>,
-        <a href="https://www.linkedin.com/in/pameeela/">Pamela Barone</a>,
-        <a href="https://nathanwyand.com/">Nathan Wyand</a>, and
-        <a href="https://www.linkedin.com/in/justin-sawyer-59b0525/"
-          >Justin Sawyer</a
+        <a
+          class="external-link"
+          href="https://www.linkedin.com/in/tung-lin-bb1745163/"
+          target="_blank"
+          >Tung Lin
+          <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
+        >,
+        <a
+          class="external-link"
+          href="https://www.geocadder.bg/en/"
+          target="_blank"
+          >Geocadder
+          <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
+        >,
+        <a
+          class="external-link"
+          href="https://www.linkedin.com/in/davidrhunt/"
+          target="_blank"
+          >David Hunt
+          <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
+        >,
+        <a
+          class="external-link"
+          href="https://www.linkedin.com/in/ellen-schwartz-614847132/"
+          target="_blank"
+          >Ellen Schwartz
+          <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
+        >,
+        <a
+          class="external-link"
+          href="https://www.linkedin.com/in/tony-jordan-pdx/"
+          target="_blank"
+          >Tony Jordan
+          <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
+        >,
+        <a
+          class="external-link"
+          href="https://www.linkedin.com/in/pameeela/"
+          target="_blank"
+          >Pamela Barone
+          <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
+        >,
+        <a class="external-link" href="https://nathanwyand.com/" target="_blank"
+          >Nathan Wyand
+          <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
+        >, and
+        <a
+          class="external-link"
+          href="https://www.linkedin.com/in/justin-sawyer-59b0525/"
+          target="_blank"
+          >Justin Sawyer
+          <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
         >. The map data come from
-        <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a>. The
-        map is built using <a href="https://leafletjs.com/">Leaflet</a>. The map
-        tiles are developed by
-        <a href="https://www.stadiamaps.com/">Stadia Maps</a>,
-        <a href="http://stamen.com/">Stamen Design</a>,
-        <a href="https://openmaptiles.org/">OpenMapTiles</a>, and Google Maps.
+        <a
+          class="external-link"
+          href="https://www.openstreetmap.org/copyright"
+          target="_blank"
+          >OpenStreetMap
+          <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
+        >. The map is built using
+        <a class="external-link" href="https://leafletjs.com/" target="_blank"
+          >Leaflet <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
+        >. The map tiles are developed by
+        <a
+          class="external-link"
+          href="https://www.stadiamaps.com/"
+          target="_blank"
+          >Stadia Maps
+          <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
+        >,
+        <a class="external-link" href="http://stamen.com/" target="_blank"
+          >Stamen Design
+          <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
+        >,
+        <a
+          class="external-link"
+          href="https://openmaptiles.org/"
+          target="_blank"
+          >OpenMapTiles
+          <i aria-hidden="true" class="fa-solid fa-arrow-right"></i></a
+        >, and Google Maps.
       </p>
       <p>Copyright 2023 Parking Reform Network - All Rights Reserved</p>
     </section>
@@ -287,6 +371,7 @@ <h3>Acknowledgments</h3>
       <a
         href="https://parkingreform.org/support/"
         aria-label="Support Parking Reform Network"
+        target="_blank"
         ><img
           src="./assets/images/prn-logo.png"
           alt="Parking Reform Network logo"