Mslogin and login on register

[jeff-zimmerman]

Added option LOGIN_ON_REGISTER (Default: False) to app_settings.py. Modified RegisterView in registration/views.py to include the option for logging in on registration. This could not be done in user code, as there is no option to subclass the Register view (only the Register serializer). It uses basically the same code as the Login view with some slight variations.

Also added social serializer for Microsoft Graph API. This can be done user side, but I though you might like to add it as a default. It subclasses SocialLoginSerializer and implements the TwitterLoginSerializer's validation scheme. This was necessary because the standard SocialLoginSerializer uses 'access_token' and 'code' to make OAuth requests, while Microsoft uses 'accessToken' (no code). Also removed the request.session setting in validate().

[jeff-zimmerman]

This passes/fails all the same tests that the main branch does.