[#74] pull dependency versions into properties

pom.xml

@@ -86,11 +86,18 @@
     <mojo.java.target>8</mojo.java.target>
     <wagon.api.version>3.0.0</wagon.api.version>
 
+    <!-- Test plugins -->
     <takari-plugin-testing.version>2.9.2</takari-plugin-testing.version>
     <takari-lifecycle-plugin.version>2.0.0</takari-lifecycle-plugin.version>
 
-    <ftpserver.version>1.1.1</ftpserver.version>
     <project.build.outputTimestamp>2022-01-18T09:14:02Z</project.build.outputTimestamp>
+
+    <!-- logging -->
+    <dependency.slf4j.version>1.7.9</dependency.slf4j.version>
+
+    <!-- Test dependencies -->
+    <dependency.jetty.version>9.4.51.v20230217</dependency.jetty.version>
+    <ftpserver.version>1.1.1</ftpserver.version>
   </properties>
 
   <dependencies>
@@ -181,12 +188,12 @@
     <dependency>
       <groupId>org.slf4j</groupId>
       <artifactId>slf4j-api</artifactId>
-      <version>1.7.9</version>
+      <version>${dependency.slf4j.version}</version>
     </dependency>
     <dependency>
       <groupId>org.slf4j</groupId>
       <artifactId>slf4j-simple</artifactId>
-      <version>1.7.9</version>
+      <version>${dependency.slf4j.version}</version>
       <scope>test</scope>
     </dependency>
 
@@ -219,13 +226,13 @@
     <dependency>
       <groupId>org.eclipse.jetty</groupId>
       <artifactId>jetty-server</artifactId>
-      <version>9.4.51.v20230217</version>
+      <version>${dependency.jetty.version}</version>
       <scope>test</scope>
     </dependency>
     <dependency>
       <groupId>org.eclipse.jetty</groupId>
       <artifactId>jetty-http</artifactId>
-      <version>9.4.51.v20230217</version>
+      <version>${dependency.jetty.version}</version>
       <scope>test</scope>
     </dependency>
   </dependencies>