Fix a regression introduced by the ability-to-exclude-tags patch, and make some stuff work (again):
- use a special "add exclude" mode only enabled in models that need it. Fixes regression 267421
(partial check state treated as fully checked)
- albumDecorationRole is overridden by derived classes, so there is no sense in doing the overlay
painting in this method in the parent class. Provide a tool method which is called from the children,
now the + or - is visible.