Fixed Data-Race issue where DefaultBounds were incorrectly cloned when
cloning an image. This datarace caused undefined behavior that is now
corrected and helps with rendering Opacity Keyframes.

Added a new KisDefaultBoundsNodeWrapper class to handle bounds accessing
and checking inside of keyframe channels. This allows for easier copy
constructors for KisKeyframeChannels and helps keep data pointer logic
more consistent.

Now, when images are cloned, they are always pointing to the correct
time index.