Implemented avoid_crossing_perimeters with VisiLibity
Update MANIFEST and test
Merge branch 'master' into visilibity

Conflicts:
	lib/Slic3r/GCode.pm
	xs/MANIFEST
Fix MANIFEST
Simplify islands before initializing MotionPlanner
New implementation of Avoid crossing perimeters using Voronoi diagrams
Bugfix: make_perimeters() was not truly idempotent because prepare_infill() split ->slices into typed surfaces
Fixed recursion in background processing
Display bed shape in 3D plater
Correct Z positioning of multiple objects in 3D plater
Bugfix: ignore only_retract_when_crossing_perimeters when fill_density = 0
Fixed minor regression in cut dialog
Change default layer height to 0.3mm
Relax collision checks when Detect thin walls is disabled
Bugfix: some extra spots were added in medial axis
Display skirt and brim in toolpaths preview. Also take support material margin into account when sizing the window. #2169
Put skirt outside brim to avoid conflicts. #2157
Allow configuration of G-code origin for rectangular bed shape
Bugfix: seam_position = aligned/nearest didn't work correctly for hi-res models. #2156

Conflicts:

	lib/Slic3r/GCode.pm
New utility script to convert config bundles into a single config file