Fix crash with running animators on re-shown windows.

The non-threaded render loops would clean up the nodes for a window
when it was hidden, but the animators kept running and had a reference
to the deleted nodes. This was not a problem for the threaded render
loop as it would wipe the animator controller as well which would
clean the jobs.

Fix it by triggering a reset of all nodes in the animators when the
window is told to clean up. If an animator is ticked when it doesn't
have a node, it will simply do nothing. When the window is made visible
again, we call initialize on all animators to find the new node.

Task-number: QTBUG-37995
Change-Id: Ie5609d95db29f4b2b30ca5bf641dce901e528389
Reviewed-by: Michael Brasser <michael.brasser@live.com>