Remove getTeams function

as it is not user management specific
Update DB scheme

and refactor the classes to match the updated scheme.
Fix code style
Refactor atLeast function

to respect the suggested changes boom1992.

See: https://github.com/Paperdreamer/userManagement/pull/2#discussion-diff-13260555
Merge pull request #2 from tobiasmuecksch/master

Update database scheme
Fix broken session handling
Merge pull request #3 from tobiasmuecksch/master

Fix broken session handling
Add methods to get active users, suspended users, if the current user is an administrator and also activating suspended users