Jb/flat member list

My intension:
I wanted to reduce the database accesses 
by caching it or
by fetching the necessary data only or 
by reducing the complexity of data shown to the user.

My changes:
1. The computation if the user can manage a group does not longer create officers and admin groups
2. The Aktivitaetszahl and the My_Groups_Table are cached as long as a group membership of the user is commited.
3. Fixed a bug that indirect members were not unique
4. Increased Capybara default_wait_time for bundle exec rake
5. For a group show all indirect members in a flat list and do NOT show the subgroups or the user group membershio for subgroups
6. Show officers if there are any officer sub groups
7. Do NOT show links for each officer.

The effect:
The most group pages last 2 seconds instead of 4-6 seconds. The "WingolfAmHochschulort" group is loadable.