-RM-347-MR-Extend WUI to allow nesting CustomWidgets in CustomWidgets via an abstact grid layout.
Create an abstract grid layout to allow adding custom views into this grid. The grid the can be used in an abstract custom widget. The Qt4 GUI can implement this easily. Non-graphical UIs can safely ignore these features.
(from redmine: created on 2014-03-27, closed on 2014-04-11, blocks #341 (closed))