iconGrid: Dynamically adjust spacing based on columnLimit

Adjust the spacing based on the available width when a columnLimit
is set to evenly place the icons.

https://bugzilla.gnome.org/show_bug.cgi?id=694215

js/ui/appDisplay.js

@@ -63,6 +63,9 @@ const AlphabeticalView = new Lang.Class({
         this._grid = new IconGrid.IconGrid({ xAlign: St.Align.MIDDLE,
                                              columnLimit: MAX_COLUMNS });
 
+        // Standard hack for ClutterBinLayout
+        this._grid.actor.x_expand = true;
+
         this._items = {};
         this._allItems = [];
     },