Clear the data when the model resets.

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>
Fixed item visibility on emptyState after being on profileState.

Background was not correctly back to it's original position
and a few other items kept their visibility when it shouldn't.

Signed-off-by: Tomaz Canabrava <tcanabrava@kde.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Do not add the items to the scene twice.

Those items have parent(), which means that when the parent has a scene,
they are automatically added and removed from the scene.

Signed-off-by: Tomaz Canabrava <tcanabrava@kde.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>