[views/favabstracts] Tooltip over dis/favour icon

Closes #420

Author: mpsonntag

app/views/abstractlist.scala.html

@@ -86,10 +86,16 @@ <h4 class="list-group-item-heading" data-bind="text: title"></h4>
 
             @if(account.isDefined) {
                 <li data-bind="visible: !$root.isFavouriteAbstract()">
-                    <a class="favour" data-bind="click: $root.favourAbstract" href="">&#9733</a>
+                    <a class="favour gn-tooltip" data-bind="click: $root.favourAbstract" href="">
+                        &#9733
+                        <span class="gn-tooltiptext">Add abstract to favourites</span>
+                    </a>
                 </li>
                 <li data-bind="visible: $root.isFavouriteAbstract">
-                    <a class="disfavour" data-bind="click: $root.disfavourAbstract" href="">&#9733</a>
+                    <a class="disfavour gn-tooltip" data-bind="click: $root.disfavourAbstract" href="">
+                        &#9733
+                        <span class="gn-tooltiptext">Remove abstract from favourites</span>
+                    </a>
                 </li>
             }