GWT emulate https://github.com/libgdx/libgdx/commit/c4c0db96097ee51ebdda6de7b2c40a2fd4386e8d
Node, deprecated children and parent, added inheritTransform flag and methods to add/get/remove children
Add line to CHANGES for Node#children/parent deprecation
Implement pause and resume calls for GWT
Use AnimationScheduler instead of Timer

Closes #2289, #2290
Reference instead of copy keyframes to avoid bloating