Visibility groups: also record visibility states of renderer categories (legend nodes) into groups

Visibility of a layer is not stored within the map layer, but visibility
of renderer categories (which turn into legend nodes) is stored inside renderer and
that one in turn inside map layer. This fact may result in surprising behavior
when change of visibility group for a composer map will affect other composer maps (and main canvas).
The only way to overcome the problem would be to have the possibility to use multiple renderers with one layer.