WIP tags: REST API addition

@greut I agree with you on the theoretical level. However, in practice running the tests during development several times managed to create several users with the same nickname (because the User model is in heavy need of refactoring!). Hence, this is a practical work around because no one have dared to refactor the User model yet (feel free to take a stab). So, this is a very minor issue compared to that the User model allows users with identical nicknames to be stored in the database!