Case-insensitive authentication in Poulpe

As a User I'd like to be able to log in to Poulpe without warring about case of the letters so that it's easier to log in to JC & Antarcticle.

Acceptance Criteria

• In case username is unique 
  • If user logs in via UI, it's not important what case of letters he uses
  • If we get info about the user via REST service, then it's not important what case is specified in the GET request
• In case there are already 2 or more users with the same username that differs only in letter case
• Then authentication is case-sensitive and exact match of username is expected
• While authentication via REST, the user information should be returned in response in exact form it's kept in Poulpe DB (the case of letters is returned as is)