Navigation palette: thumbnails isn't refeshed after application added to the page

The annotations are erased when you select the Erase items

The annotations are erased when you select the Erase items

Code was cleaned.
Corrections in removing strokes.

Corrected adding items to group.
Corrected group creation.
Corrected adding items to scene - items shouldn't be added to itemsToRemove list because that list needs for cleaning undo stack.
Improved mechanism of removing "itemsToRemove".
Removed wrong deletion of mButtons list from UBGraphicsItemDelegate destructor because that buttons has Frame as parent.
Removed possible memory leak in UBBoardController::clearUndoStack. Some items was able not deleted.
tmpScene in cffReader not deletes now because ithas a proxy as parent.

Improvement of scene update flag setting

Fixed some related issues.