rspec: adding the fuubar gem to have a better progress bar when running specs with guard and rspec.
rspec: adding the possibility to login as local admin.

Use: `login(:local_admin, of: @group)`

For the moment `login(:admin)` will grant global admin rights.
issue: Local admins can't execute workflows.

Reproducing this issue by running the specs for local admins.

Trello:
https://trello.com/c/l36wSJJh/666-fix-lokale-admins-konnen-keine-workflo
ws-ausfuhren
fix: Local admins now can execute workflows

The authorization of the execute action did not work properly on the
controller level.

trello:
https://trello.com/c/l36wSJJh/666-fix-lokale-admins-konnen-keine-workflo
ws-ausfuhren
fix: Local admins now can manage users' memberships.