Allow for animation inside FBOs for masking/caching nodes

[vtron]

FBOs right now create memory leaks when changing sizes (in Cinder), so resizing FBOs needs to be avoided at all costs.

Masking right now is a 1 time cache operation, but this means nodes can not be redrawn. We should at least have a Rectf argument (defaults to current bounds) so that animtion can happen inside the mask. We could possibly use the size of the mask itself but this creates issues with movement of the mask