Update DB scheme

add unique key to User.Name and change the default value of User.Suspended to 1.
Fix broken createUser function
Implement getSession function
Refactor login method

to throw an exception if a suspended user tries to log in.
Merge pull request #5 from tobiasmuecksch/master

Fix broken registration
Fix broken getSession function
Refactor login method

to return if a particular user is an administrator.
Merge pull request #6 from tobiasmuecksch/master

Refactoring regarding user factory implementation
Merge branch 'master' of https://github.com/paperdreamer/userManagement into upstream/master
Remove method to get admin state