Separate :class:.Animation and :class:.Scene

[JasonGrace2282]

Motivation

• Long term goal of experimental is to render animations in parallel
  • A big part of this is removing the direct usage a Scene in an Animation.
• Also it helps to be able to know the bare minimum amount of methods needed to animate something, so I got started with a simple AnimationProtocol.

Implementation

TL;DR: an Animation stores what actions it wants to do to the Scene. During the start of the animation and end of animation, the Scene checks those actions and applies them.

Long Explanation: attached to each Animation object is a buffer attribute (of type SceneBuffer: you can think of this as an extremely simplified proxy of Scene that stores add and remove operations). Whenever an animation wants to, say add a mobject to the scene they would do self.buffer.add(Square()).
For each animation in a self.play call, the Scene will call the begin method and then "apply the buffer". It is at this time that the adding/removing of mobjects actually happens. Likewise with when the animation finishes.

TODO

• Implement core SceneBuffer stuff
• Fix subclasses
• Finish AnimationProtocol