UserMixin.tokens naming

[dbrgn]

In social.storage.base there is a property called tokens. In django-social-auth this used to return a dictionary containing different token types.

Now it returns the access token:

@property
def tokens(self):
    """Return access_token stored in extra_data or None"""
    return self.extra_data.get('access_token')

The pluralized naming doesn't really make sense though. What about deprecating tokens and moving the functionality to an access_token property?

[omab]

Change implemented, thanks!