Control AMIV wiki access

Created by: temparus

As of now, all groups have to be manually configured for access to the internal AMIV Wiki. Most groups would need access to the wiki, so this is kind of silly work.

We could add a flag like restricted_access to the groups entity. This is kept very general and can be used by various tools only differentiating between active and passive member.

What do you think about that? @NotSpecial @hermannsblum @cburchert