[appDisplay] Unify Inactive/RunningWellItem, split into AppIcon, AppWellIcon

The distinction between the inactive and running was silly; just
have one class which can handle both running states.  However for
a future search patch, we do want a separation between an icon which
just has icon + name + glow, and a well icon which does the menu
integration.

https://bugzilla.gnome.org/show_bug.cgi?id=603523

js/ui/overview.js

@@ -248,7 +248,7 @@ Overview.prototype = {
     // This allows the user to place the item on any workspace.
     handleDragOver : function(source, actor, x, y, time) {
         if (source instanceof GenericDisplay.GenericDisplayItem
-            || source instanceof AppDisplay.BaseWellItem) {
+            || source instanceof AppDisplay.AppIcon) {
             if (this._activeDisplayPane != null)
                 this._activeDisplayPane.close();
             return true;