Editor: Instance editing mode - rotate sub mode
Rotate selected instance with primary/secondary edit drags. See the tooltip of the rotate sub-mode for details. Drag originating on one of the selected instances should rotate the objects based on the camera viewing direction.
Additionally while in rotate mode selected instances should have a marker rendered on top of them (see red/green/blue rings in screenshot, taken from blender). The rings should be aligned to the global coordinate system. Drags that originate on one of the markers should rotate the instances along the axis defined by this marker exclusively.
Note: This task requires a properly working camera to be implemented first.
(RM-3166 from redmine: created on 2016-01-26 by Marc Zinnschlag, , closed on 2016-08-18 by Kyle Cooley, relates #3000 (closed), relates #3245 (closed))