Add support for X-GOOGLE-TOKEN.

This is mainly just useful for authenticating without using TLS.

If an access token is not provided, an attempt will be made to
retrieve one from Google.

sleekxmpp/thirdparty/suelta/mechanisms/__init__.py

@@ -5,3 +5,4 @@ from sleekxmpp.thirdparty.suelta.mechanisms.digest_md5 import DIGEST_MD5
 from sleekxmpp.thirdparty.suelta.mechanisms.scram_hmac import SCRAM_HMAC
 from sleekxmpp.thirdparty.suelta.mechanisms.messenger_oauth2 import X_MESSENGER_OAUTH2
 from sleekxmpp.thirdparty.suelta.mechanisms.facebook_platform import X_FACEBOOK_PLATFORM
+from sleekxmpp.thirdparty.suelta.mechanisms.google_token import X_GOOGLE_TOKEN