Add OAuthTestsMixin and OAuth2TestsMixin.
Add OAuthTestsMixin and OAuth2TestsMixin.

These replace create_oauth_tests and create_oauth2_tests going forward,
though those calls remain intact for backward compatibility with
third-party providers.

lukeburden/django-allauth,lukeburden/django-allauth,pennersr/django-allauth,AltSchool/django-allauth,rsalmaso/django-allauth,joshowen/django-allauth,agriffis/django-allauth,pztrick/django-allauth,bjorand/django-allauth,jwhitlock/django-allauth,agriffis/django-allauth,bittner/django-allauth,bittner/django-allauth,pennersr/django-allauth,spool/django-allauth,bjorand/django-allauth,wli/django-allauth,wli/django-allauth,nimbis/django-allauth,lukeburden/django-allauth,jwhitlock/django-allauth,agriffis/django-allauth,joshowen/django-allauth,rsalmaso/django-allauth,jwhitlock/django-allauth,spool/django-allauth,nimbis/django-allauth,joshowen/django-allauth,wli/django-allauth,pztrick/django-allauth,bittner/django-allauth,spool/django-allauth,AltSchool/django-allauth,pennersr/django-allauth,AltSchool/django-allauth,nimbis/django-allauth,rsalmaso/django-allauth,pztrick/django-allauth,bjorand/django-allauth