Refactor high-level renderer

[ ] Ensure that renderer system is not using mesh/material/texture resource directly.
[ ] Move the high-level renderer code to another project (e.g. nfRenderer):
- nfCore/Renderer/ can be just moved
- RendererSystem must be split into RenderSystem (wrapper for HL-renderer) and RenderScene (or something)
[ ] Create "Demo" application for testing high-level features without nfCore (lights, shadows, meshes, post-process, etc.)
[ ] Ideally, low-level renderer (backend) interface should not be visible by the nfCore/demo app.

The biggest problem will be to extract code from RendererSystem and View classes

nfprojects / nfengine