GUACAMOLE-723: Move getClientIdentifier() to GroupListItem for convenience of other uses of the guacGroupList directive.

guacamole/src/main/webapp/app/home/templates/connection.html

@@ -1,5 +1,5 @@
 <a class="home-connection"
-   ng-href="#/client/{{context.getClientIdentifier(item)}}"
+   ng-href="#/client/{{ item.getClientIdentifier() }}"
    ng-class="{active: item.getActiveConnections()}">
 
     <!-- Connection icon -->