Makes some links open in new tabs #60

[Lucas-Mc]

Changes some links to open in a new tab. Specifically, the links in the footer and the continue reading links were changed. Direct links to other pages in the navbar are unchanged. Fixes part of #60.

[tompollard]

I'd avoid new window pop-ups altogether, but if we want to use them we should try to be consistent with how they are used. One simple distinction is for new windows to be used only for external links.

In this pull request, some of the internal pages open in new windows (e.g. "Continue reading), while others don't, which is confusing.

It would be good to draw attention to links that open in new windows, either with some "opens in new window" text or an accessibility icon. On PhysioNet we use this:

a[target='_blank']::after {
content: '\29C9';
padding: 0em 0.15em;
}

[tompollard]

Looking at the W3C recommendations on links opening in new windows at: https://www.w3.org/TR/WCAG20-TECHS/G201.html, they suggest that:

Opening new windows automatically when a link is activated can be disorienting for people who have difficulty perceiving visual content, and for some people with cognitive disabilities, if they are not warned in advance.

This page highlights some issues with popping up pages in new windows: https://accessibility.oit.ncsu.edu/it-accessibility-at-nc-state/developers/accessibility-handbook/mouse-and-keyboard-events/links/links-and-new-windows/