GUAC-586: Clarify auth result and include data source. Consistently refer to usernames as "username", not "user IDs".

guacamole/src/main/webapp/app/navigation/directives/guacUserMenu.js

@@ -78,7 +78,7 @@ angular.module('navigation').directive('guacUserMenu', [function guacUserMenu()
              *
              * @type String
              */
-            $scope.username = authenticationService.getCurrentUserID();
+            $scope.username = authenticationService.getCurrentUsername();
             
             /**
              * The available main pages for the current user.