* 1. Remove all global include_directories.
* 2. Move 3d party dependencies from src to budled deps if possible.
* Unify and enforce one way of including headers:
e.g. #include "libslic3r/GCode.hpp" vs #include "GCode.hpp"
(always use the "libslic3r/GCode.hpp" option).
* Make all dependencies (also header only) a cmake target.
If there are only 2 or 3 perimeters on a layer, exactly two of them are
external and just one of them is a hole, then the seams should be
choosen next to each other on the external perimeters.
Previously there was an algirithm that was fitting a curve through
the resulting seam points. This worked for smooth models, but was
failing for some very basic cases (such as a cylinder).
The new algorithm builds on the previously implemented visibility
algirithm but does not do the curve fitting anymore.
Now the code is more separated for the four seam placement
options (rear, random, aligned, nearest).
Nearest and random are handled as one would expect.
Aligned is handled in a more "brute force" manner
(trying multiple seams and picking the best one)
and rear smartly switches between two modes
(center straight line projection and max y).
