added entities missing for the group concept
added missing tree type to group
cleaned some code
rearranged parameters in PermissionVoter
added UserGroups to PermissionVoter
updated UserRepository to include groups from users
added groups to user controller
added GroupController
cleaned code
code review & cleanup
Merge branch 'feature/security-groups' into develop
Merge branch 'feature/navigation-2.0' of git://github.com/sulu-cmf/SuluSecurityBundle into feature/navigation-2.0