Implement cache property for QQuickAnimatedImage

Implement cache property for QQuickAnimatedImage

Some longer and larger .gifs can consume a lot of memory
if every decoded frame is cached. Just as the backing QMovie
provides the ability to not cache frame, so should AnimatedImage.

This also allows a workaround for some animated image types
that can contain loops that aren't handled correctly (QTBUG-24869)
to not leak memory.

Change-Id: I0639461d75bb2c758917893e7a6ae5c215fffa9d
Task-number: QTBUG-44447
Task-number: QTBUG-24869
Task-number: QTBUG-28844
Reviewed-by: Alan Alpert <aalpert@blackberry.com>