Changed account alias for token generator

Previously, it was `username@sitename`; however as the username can also
contain an e-mail address, the identifier would contain two at signs. To
overcome this, it has been changed to `sitename (username)`. Thanks to
Edward D'Souza for reviewing the custom user model support.
Renamed tox's custom user model test suites
Added a list of all contributors

To add your name, submit a pull request or ping me.
Next release will be 0.6.0
Pulled new/updated translations
Cleaned up release notes