fix broken links (mostly in A2 MeshEdit)

Downgrade CMake 3.17 -> 3.16 for CLion IDE users to build the project and enjoy intelligent code completion

Features
- Button to add samples to current render

Fixes
- Don't draw emitter arrows when rendering with rasterization
- (Previous commit) deal with non-uniform ray hit distance scaling
  systematically instead of deferring it to hit functions.