Edx-auth-backends

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Two new commits that changed functionality:

- Add EdXOAuth2.auth_complete_signal on auth_complete()
- Store refresh_token in extra_data

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Create new Version for auth-backends for release

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EdXOAuth2 will retrieve and store user_id claim

The EdXOAuth2 backend will now pull the user_id from the JWT and
store it in the UserSocialAuth.extra_data field.

BREAKING CHANGE: The user_id scope is now required when using the
EdXOAuth2 backend for oAuth+SSO. This means that the oauth
application must first be configured to have access to the user_id
scope, which is not available by default.

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Updates to the EdXOAuth2 backend:

- Supports the _PUBLIC_URL_ROOT social django setting.
- logout_url() allows _LOGOUT_REDIRECT_URL to be undefined.

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Fix urlencode bug with EdXOAuth2 backend logout url

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Allow for logout redirect with EdXOAuth2 backend.