NavigationController: Don't handle scroll wheel events if the view isn't enabled.
widgets: export: Added basic dvid support, but with rough edges.
dvid export ui: cleanups.
ShortcutManager: Purge old shortcuts from the list after they or their targets have been deleted.
TODO: This should really be fixed by refactoring the shortcut management system.
Applets or workflows should be allowed to delete entire groups of shortcuts during their cleanup process.
layerwidget: Fixed manual quicktest.
bring back Viewer.title property
quadsplitter: Remove unecessary widget
Added volumina.NO3D flag, which allows clients to disable 3D support for testing purposes.
If volumina.NO3D flag == True, VTK is not even imported.
ImageView2D and VolumeEditor constructors now require a parent arg.
layerwidget: Use persistent editors.
This simplifies certain event handling, and also works much better with the eventcapture testing framework.