Add OAuth2 capabilities

OAuth2 finally landed in Nuxeo Drive! Support for OpenID Connect Discovery and ADFS were implemented too. A bunch of new options are now available to customize OAuth2 connection: [oauth2-authorization-endpoint] ( https://doc.nuxeo.com/client-apps/nuxeo-drive/#oauth2-authorization-endpoint ), [oauth2-client-id] ( https://doc.nuxeo.com/client-apps/nuxeo-drive/#oauth2-client-id ), [oauth2-client-secret] ( https://doc.nuxeo.com/client-apps/nuxeo-drive/#oauth2-client-secret ), [oauth2-scope] ( https://doc.nuxeo.com/client-apps/nuxeo-drive/#oauth2-scope ) and [oauth2-openid-configuration-url] ( https://doc.nuxeo.com/client-apps/nuxeo-drive/#oauth2-openid-configuration-url ). Set revelant ones in the local configuration file before starting the application. For now the legacy Nuxeo token authentication is still the default. To use OAuth2, first add a [OAuth2 consumer] ( https://doc.nuxeo.com/nxdoc/using-oauth2/#client-registration ), then when adding a new account in Nuxeo Drive, simply uncheck the "Use legacy authentication" checkbox. Related tickets: NXDRIVE-2627 and NXDRIVE-2403 .