[Layout] Cache reference to body later in mct-drag

Get a reference to the body element at link-time,
instead of instantiation time, from the mct-drag
directive. Failure to do so causes the reference
to fall out of date when switching between Browse
and Edit mode.

Supports position/sizing interactions for Layout
view, WTD-535.

platform/commonUI/general/src/MCTDrag.js

@@ -6,10 +6,10 @@ define(
         "use strict";
 
         function MCTDrag($document) {
-            var body = $document.find('body');
 
             function link(scope, element, attrs) {
-                var initialPosition,
+                var body = $document.find('body'),
+                    initialPosition,
                     currentPosition,
                     delta;