by @supermerill and @wavexx
WIP: The function Fill::connect_infill() is being rewritten
to utilize spatial structures wherever possible for lower CPU load
and less dynamic memory allocation.
for islands with another islands in their holes.
Improvement of chaining of infill lines for 3D honeycomb, Gyroid and
Honeycomb infill: New TSP chaining algorithm is used.
When generating patterns which are less than a full wave, always
generate the last point correctly.
When extending a full wave to a line, fixup the last point
to the real gyroid position instead of shifting the point.
Changes in SupportMaterial.cpp, TriangleMesh.cpp and 01_trianglemesh.t
are yet to be merged.
WIP: Refactoring of layer height editing.
Removed layer_height_ranges from PrintObject, as the Print/PrintObject
now hold their copies of Model/ModelObject.
