Updated the relationships name in umessages

- Updated "to_user" in "um_user_to"
- Updated "from_user" in "um_from_user"
Updated the translation files

- Updated "to_user" in "um_user_to"
- Updated "from_user" in "um_from_user"
Merge branch 'refs/heads/umessage_namespacing'
Merge branch 'master' of https://github.com/LeonardoGentile/django-userena