Ignore CMakeLists.txt.user file.
Whitespace fixes.
Continue work on path tracer.

* Ported over a lot of code from (Veach 1997) but nothing works.
  A tons of debugging to do.
  - Old renderer is still enabled as default.
* Found and fixed a rendering bug from having point light sources be
  emulated as spheres with very small radius.
* Reworked how lights work: they are not part of the geometry.
  As a next step lights should also have material properties istead
  of fixed colour. Need to add emittance.