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to fall out of date when switching between Browse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.
Properly reset the initial drag position tracked by the
mct-drag position so that multiple drags upon the same
element are correctly offset from an initial position.
Also, preventDefault from events to avoid selection
highlights during drag.
Supports editing Layout objects, for WTD-535.
