Migrate Google authentication to OpenID Connect before April 15

[tonylampada]

Or we're gonna have a big problem

https://support.google.com/accounts/answer/6135882?authuser=2

[tonylampada]

Done.
Relevant information for whoever needs to do the same thing:
(hope google indexes this)

I migrated my django application from django-social-auth to python-social-auth, just to be able to authenticate users with openid-connect, before google discontinues it.

Relevant links:
[1] https://groups.google.com/forum/#!topic/django-social-auth/7ljo6sxdtsw
[2] omab/django-social-auth#815
[3] Don't use PickleSerializer
[4] Live with a fork of psa, for now

Thanks a lot to @omab and @cambonf - your work has been very helpful.