added qq openid connect support

https://github.com/pennersr/django-allauth/issues/628

I added qq support to allauth and would like to contribute it to this project.

It's based on the weibo/oauth2 provider.
QQ requires you to obtain an openid before being about to access their apis. I decided to use the openid as the uid since there is no id string in extra_data.
To add this I created an openid_connect provider that inherit from classes in the oauth2 app.