fix(activator): properly activate elements nested inside an item.

Addresses #1373.

Before: if an `<a>`, `ng-click`, or `<button>` inside of a .item,
was clicked, the activator would walk up .item and activate it.

Now:  If an `<a>`, `ng-click`, or `<button>` inside of a
.item is clicked, the activator will activate that element.

Additionally, CSS was added so `a.item-content.activated` would look
activated.

test/html/list.html

@@ -49,6 +49,14 @@
   		<div class="item item-divider">
   		Type 1
   		</div>
+      <ion-item href="#">
+        <button class="button button-energized">
+          Hello
+        </button>
+      </ion-item>
+      <ion-item href="hello">
+        Woah!
+      </ion-item>
         <ion-item ng-repeat="item in items"
                   ng-click="alert(item.id)"
                   class="item item-avatar-left item-icon-right"