This is the first step of refactoring Animation where it is needed
to separate AnimationBitmap(s) from the Animation class, which
is also responsible for displaying of animation.

General idea is to make Graphic work only with AnimationBitmaps,
which can be freely be swapped out and in, make copies - all
transparantly from the actually displaying them and possibly it
will also remove the need to copy the animation objects.

Change-Id: If5d55ac1a5b26c3880d4f7602be57742b086f9da
Reviewed-on: https://gerrit.libreoffice.org/71406
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>