Editor: Render cell border markers
In PagedWorldspaceWidget scenes the borders between rendered cells and between rendered cells and unrendered cells should be marked in some way, that is clearly visible but does not obstruct the view. At least vertical lines at the cell corners, maybe with some horizontal bars along the cell borders (these are only suggestions; other ideas welcome).
As the list of rendered cells is changed, these markers need to be added/removed automatically.
- These markers need a separate visibility flag, so that they can be switched on/off from the scene toolbar (button not implemented yet).
- These markers are not relevant for mouse picking, since the user will never interact with them. Therefore no query flag is required.
(RM-1279 from redmine: created on 2014-04-14 by Marc Zinnschlag, , closed on 2016-03-03 by Kyle Cooley)