appDisplay: Expand AllView

If the view doesn't fill the available space, content should still
start at the top rather than the center - not least the positioning
code for folder popups assumes that, so set the appropriate expand
flags.

https://bugzilla.gnome.org/show_bug.cgi?id=694371

js/ui/appDisplay.js

@@ -187,6 +187,9 @@ const AllView = new Lang.Class({
     _init: function() {
         this.parent();
 
+        this._grid.actor.y_align = Clutter.ActorAlign.START;
+        this._grid.actor.y_expand = true;
+
         let box = new St.BoxLayout({ vertical: true });
         this._stack = new St.Widget({ layout_manager: new AllViewLayout() });
         this._stack.add_actor(this._grid.actor);