rework gmail binding

[arderyp]

google is turning off Less Secure App (LSA) access, which we currently rely on to send emails: https://gsuiteupdates.googleblog.com/2019/12/less-secure-apps-oauth-google-username-password-incorrect.html

we need to mov eot the officially supported OAuth 2.0 mechanism: https://developers.google.com/gmail/api/quickstart/python

more sources to look into:

• https://github.com/vaibhavsawhney/Google-Gmail-API-Python-Django-1.9-Sample
• https://github.com/googleapis/google-api-python-client
• https://stackoverflow.com/questions/24855049/using-gmail-api-in-django
• https://developers.google.com/identity/protocols/OAuth2
• https://developers.google.com/gmail/api/auth/about-auth

[arderyp]

I believe this was resolved in Release 3.0.9

Whatever the case, we are using BCOP now, which avoids this issue. Furthermore, Gmail seems to have halted their plan to disable LSA:

Update 
March 30, 2020: We have suspended the turn-off detailed here until further notice. We'll announce new timelines on the G Suite Updates blog at a later date. For more details,

https://workspaceupdates.googleblog.com/2019/12/less-secure-apps-oauth-google-username-password-incorrect.html