Completed the TODO in models/user.rb "Move to ArchiveConfig"

Branch doesn't match the ticket because i created the branch before adding the ticket. 

Ticket this commit closes: https://code.google.com/p/otwarchive/issues/detail?id=3699

Changes made 
Moved the Following lines
TODO: move to ArchiveConfig
 LOGIN_LENGTH_MIN = 3
 LOGIN_LENGTH_MAX = 40

  PASSWORD_LENGTH_MIN = 6
 PASSWORD_LENGTH_MAX = 40

To config.yml . These constants can now be referenced by the ArchiveConfig class. 

Updated the existing invite_queue.feature to account for too long password and login. 

Also refactored the users tests in models/user_spec.rb The tests related to password validation are passing.