Make OpenGL optional for the new parts dialog. #1731
Regression test and incomplete fix for bug affecting wrong spiral vase output. #1773

Conflicts:

	lib/Slic3r/GCode/Layer.pm
Fixed spiral vase regressions. Includes regression tests. #1773
Updated test count in t/shells.t
Fix regression about percent extrusion width not being validated. Includes regression test
Refresh plater canvas when switching presets
Mark strings as UTF-8 when passing them to Perl
Use a plain list instead of a tree to display object parts
Minor layout changes to the Parts editor
Some incomplete work for per-region config
Write material config to AMF files. Remove the old Materials tab. Update custom settings when a part is selected
Fixed regression when using --infill-only-where-needed. Includes regression test. #1721
Fix crash reported by Simooon on #Slic3r.

Error was:

  Argument "" isn't numeric in subroutine entry at
    lib/Slic3r/GUI/OptionsGroup.pm line 392
Revert "Fix crash reported by Simooon on #Slic3r."

It turns out this helped on the version of stable I was using
but not on master.

This reverts commit 8df6e2d930e3a295ed1447390988c9a08f07a949.
Add stable branch to Travis CI
Regression test for #1808 (crash when using non-consecutive extruders), already fixed in master branch
Use bridge speed for first solid layer above sparse infill. Includes unit test. #1792
Better pruning of thin walls to avoid unwanted extra extrusions. Includes regression test. #1794

Conflicts:

	lib/Slic3r/Layer/Region.pm
Removed debugging line
Fix failing test after recent changes to thin wall thresholds