Added 'Cancel' button on the export stl/gcode window in print queue
commit to merge
Merge remote-tracking branch 'upstream/development'

Conflicts:
	PrintQueue/PartsSheet.cs
Making it a bit clearer.
Reversed the queue <-> library default locations
Merge branch 'development' of https://github.com/MatterHackers/MatterControl into development
Merge remote-tracking branch 'Greg/master' into development