Fixed Issue#563

Copies of a Sprite share the image files for their looks with the original Sprite because the image files themselves are not copied (expected behaviour).

The usage count for those image files was never increased and therefore the image files were deleted if deleted in one of the copied Sprites.

This has been fixed.

Jenkins run:
http://jenkins.catrob.at/job/Catroid-Multi-Job-Custom-Branch/142/

http://jenkins.catrob.at/job/Catroid-single-UI-emulator/111/

http://jenkins.catrob.at/view/Catroid/job/Catroid-single-UI-emulator/112/