A series of DisplayNode <-> RenderingContext refactoring.

Moves rendering work from DisplayNode to RenderingContext.

- Phase 1: moves DisplayNode rendering functions to RenderingContext.
- Phase 2: More DisplayNode rendering work on RenderingContext.
- Phase 3: Moves setTransform from Layer to RenderingContext.
- Small refactoring to simplify the structure.
- Removes unused Layer parameter from args.
Merge branch 'refactor/rendering_context_display_node' into feature/streaming

Conflicts:
	src/Eye/DisplayNode.jsx
	src/Eye/RenderingContext.jsx
Tiny refactoring.