Refactor CanvasOverlay to be its own class, make generic Canvas

[ShrimpCryptid]

Use Case

With the new 3D viewer, CanvasOverlay should no longer extend ColorizeCanvas but instead hold a reference to an abstract canvas.

Acceptance Criteria

• Create an abstract Canvas that specifies shared canvas functionality (set parameters, getFrame, render, return DOM object)
• ColorizeCanvas should extend/implement the abstract Canvas.
• Change CanvasOverlay to be its own class that has a reference to an abstract Canvas.

Details

Would be easier if #502 is implemented