[Starts #41756255] Shows additional information about a group

This enables the #show action on the groups controller, to — possibly —
view more information about the group.

Access to view information about the group is restricted to members of
said group.
Allow administrator to update name and description for the group
Changing the way characters access groups while offgame
Ignore spec coverage
Improve group administration

This adds several tests to test the different levels of group
administration.
Passes test failing due to missing flash notice
Passes test for flash notice when removing member from group
Improve group tests when creating a new class
Improve group tests, when removing a group member
Joining a group adds you as a non-admin
[Finishes #41756255 #41756477] Updates the documentation
Merge pull request #18 from ekampp/features/admiinistrate_groups

[Delivers #41756255 and 41756477] Allows administration and selection of groups