[BREAKING CHANGE] Remove $document cache from target

We have enough teardown issues without caching a jQuery selector
from 4 levels above. This would also be a pain to manage on a target
with multiple surfaces.

Also mostly being used for #focus which can be done more
properly with ce.Surface#focus.

Breaking change: targets no longer have a $document property,
use .surface.getDocument().getDocumentNode().$element instead
or .surface.getView().focus() for focussing.

Change-Id: I8d8047df9bf340003174a090ae280a34c1086179
Merge "[BREAKING CHANGE] Remove $document cache from target"