[WIP] Add OIDC via mozilla-django-oidc

[aalexanderr]

This is something we use at scancode.onap.eu

mozilla-django-oidc is a minimal lib and does not implement stuff like:

• verify e-mail
• connect multiple accounts to single django account

this solution creates a user with preferred_username as username which might not be unique by default (mozilla-django-oidc) username is a hash of e-mail (im not 100% sure but its not important)

I'm currently testing different solutions (django-allauth, python social login) that would handle above but thought to submit this as a follow up to #336 as we are currently using it