add login/registration via facebook

[niksauer]

[niksauer]

@BIGPen1s

login test:
https://www.facebook.com/v2.12/dialog/oauth?state=rwjorjwoijr&redirect_uri=http://localhost:8080/user/login/facebook/success&client_id=166548023972530

https://developers.facebook.com/docs/facebook-login/permissions/#missingperms
https://developers.facebook.com/docs/facebook-login/manually-build-a-login-flow?locale=en_US#checktoken
https://developers.facebook.com/docs/facebook-login/access-tokens/#apptokens
https://developers.facebook.com/apps/166548023972530/dashboard/

[niksauer]

https://stackoverflow.com/questions/23807587/best-practice-to-create-a-new-account-with-facebook-login-users