- merge all -> merge all polyhedra into one (with several connected components)
- use the signal QMenu::aboutToShow() to enable/disable some menu entries.
- check that display list is deleted when destroys one entry
- The cut plugin has memory leaks. And the AABB tree item should be updated
  when the corresponding items are changed().

Clean up loading:
- DONE plugin aware
- DONE recently used history

Error handling:
- DONE currently error handling is strewn all about,
  using exceptions to report error would make that a little less complicated

Naming:
- naming of most classes is awkward and painfully verbose, especially
  prefixes suffixes

Rendering:
- rendering modes are somewhat backwards
- move rendering modes and rendering into the items

MainWindow:
- "selected" etc. needs some clean-up

Color bug:
- multiple items mess up coloring

Usability:
- DONE build context menus interactively
- make selection mechanisms more interactive

Plugin registration:
- remove from MainWindow.ui the registration of optional plugin, i.e. addaction (otherwise it's not an optional plugin)
- each plugin should store a pointer per action
- remove the action map from plugin helper
- change bool applicable() to void applicable(QList<QAction*>& visible,QList<QAction*>& invisible) to enable action of plugin one by one (only for nef for now)
- clean up  

Check what can be pulled in from experimental Mesh_3-protecting branch

related to the MERGE with Point_set_demo:
 - clean up Point_set_3.h and UI_point_3.h
 - we should probably have a points_item
 - Points and normal should be seperated items (pb with select and remove)
 
