Using the Sutherland-Hodgman algorithms convex and concave subject polygons can be clipped
by convex clip polygons.
For now we only need clipping to rectangles (Box), so limit our implementation to that. If needed this can be
trivially extended to convex clip polygons (a check whether the clip polygon is actually convex has to be added).
If convex clip polygons are needed we have to switch to e.g the Vatti algorithm.
With this commit a unified structure for includes is introduced.
The general rules:
* Only include what you need
* Include wherever possible in the cpp and forward-declare in the header
The includes are sorted in a local to global fashion. This means for the include order:
0. If cpp file: The corresponding h file and an empty line
1. Includes from the project sorted alphabetically
2. System/library includes sorted alphabetically
3. Conditional includes