Refactor transform masks not to discard keyframe channels on every change
The patch fixes the weird design of the transform masks. Before the patch KisAnimatedTransformMaskParameters were replaced on every transform mask change, which also replaced the keyframe channels. Which means that every undo operation would just delete the keyframe channels linked inside the node itself.
In the new design KisAnimatedTransformMaskParameters is never replaced (it is actually planned to rename it into KisTransformMaskParametersHolder or something like that). The holder just stores keyframe channels and the params and just returnes the proper paraps when requested (by fetching some information from the keyframe channels).