Groups of groups dynamic tab support

The idea would be to allow groups of groups to have tabs for object types in the children groups, recursively. For this gosaGroupObjects would need to be updated te reflect those types, and updated whenever a child group (or grandchild and so on) sees its gosaGroupObjects value change. This may or may not be built upon the foreignKey system.

Actual behavior

Groups of groups will not show user tabs for instance, unless they also contain a user directly (which is the current work-around)

Expected behavior

They should show the tabs for whichever types they contain directly or not.

See #5713