Version pixelDensity consistently

Change-Id: I06bbdc6e6869718058a796ca737668ce69802f2c
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Reviewed-by: Alan Alpert <aalpert@blackberry.com>
Refactored Animator internals

Change the design from posting events for starting and stopping
to use the scene graph's existing 'sync' point. This gives
much higher predictability and makes both ownership and cleanup
cleaner and also reduces intermediate states while events are
waiting to be delivered.

Task-number: QTBUG-34137
Change-Id: I069ac22acbddaa47925b8172ba98ac340fe9bf8d
Reviewed-by: Michael Brasser <michael.brasser@live.com>