Fully restructured navigation, making use of distance sorting and normals.

This changes the navigation to make use of normals and pre-sort surface candidates by distance. It comes with about 10% penalty in some cases, while improving with larger factors the cases where rays are missing and just exiting the setup. An improved future version may take into account the candidates' "price" in terms of frames and use sorting only for high prices.

Normals are now systematically used to filter out crossings from the wrong side. This is expected to bring benefits for increasing geometry complexity.

Restructured Vec2D and frame-specific data types in a new header CommonTypes.h