Move taiga/base/auth to taiga/auth
Move contents from __init__.py to backends.py with much more docstrings.
Change auth backends authentication on common settings.
Move taiga/base/users to taiga/users
Refactorized auth controllers.

Now controllers only have presentation logic. All domain
logic is moved to separate transactional service functions.
Add tests for auth services.
Uncomment enum34 on requirements.txt
removed unnecesary line
Changed the path of users app on dumpdata_rol.sh script
Merge pull request #33 from taigaio/auth-move

Auth module refactor.