Initialize TimelineBuffers when reset() or createSnapshop() are called.
Keep back references in renderables so that referrers can be invalidated if renderables are invalidated.
Make RenderableShapes dynamic if they have textures.

The textures may not be loaded when shapes are constructed. This means we need to invalidate the cached shapes on the GPU if textures are loaded at a later point.
Remove alpha property from Frames and only deal with ColorMatrices.
Merge.
Merge pull request #1422 from mbebenita/nat

Keep back references in Renderables