appDisplay: Align and contain collection grid with parent view

The popup of the FolderView is now contained inside
the parent view, solving the overflow of apps with a ScrollView.
Also, solved a lot of bugs in popup/FolderView calculation
of position and size.

https://bugzilla.gnome.org/show_bug.cgi?id=706081

js/ui/boxpointer.js

@@ -639,5 +639,18 @@ const BoxPointer = new Lang.Class({
 
     get opacity() {
         return this.actor.opacity;
+    },
+
+    updateArrowSide: function(side) {
+        this._arrowSide = side;
+        this._border.queue_repaint();
+    },
+
+    getPadding: function(side) {
+        return this.bin.get_theme_node().get_padding(side);
+    },
+
+    getArrowHeight: function() {
+        return this.actor.get_theme_node().get_length('-arrow-rise');
     }
 });