[Feature] Multiple envelopes on quads

This isn't important but would be nice: be able to assign more than one pos/color envelope to a quad. The quad should receive the added envelope editions to it

Usecases:
* Day and Night cycle, but stars should be flickering at night. Hard to do a flicker, when you have a 360 seconds animation cycle.
* Birds flying in backround. Wings need to flap + move with the bird (with different animation cycles)
* Rotating rays of a moving sun.
* I cannot thing of more right now :-)