Load last now valid group membership of user to get a nice breadcrumb
Navigation for users should start at last valid group of first corporation
Call sort_by( valid_from ) with default value to prevent nil
Flush cache also on destroy of UserGroupMembership
Task to cache the Aktivitätszahl for all users
Merge pull request #19 from fiedl/jb/494_cache_task

Task to cache the Aktivitätszahl for all users
some improvements on the cache:users task.
Apply code conventions, stable first navigation group for user, and improve spec
user import: Korrekturen der Import-Daten für Einzelfälle und Fehlformatierungen, sodass nun eine komplette Rekonstrukturion der hinterlegten Aktivitätszahlen möglich war.
Merge branch 'jb/477_repair_menu'
user import: fixing date conversion issue, W52570.
user import: adding date correction for April 31st.
Call profile fields controller with correct args