This patch does a few things:
1 - reset the model when user closes the dive file
2 - connects the 'rowsAboutToBeRemoved' in a way that the graphics can
remove their polygons too
3 - adds a 'clear' virtual method so items that don't follow the rules can
clean themseves up.
Signed-off-by: Tomaz Canabrava <tcanabrava@kde.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>