Fix XEP-0078 using the new stream feature workflow.

Honestly, this is mainly just a demo/proof of concept that we
can handle dependencies and ordering issues with stream features.

DON'T use XEP-0078 if you are able to use the normal SASL method,
which should be the case unless you are dealing with a very old
XMPP server implementation.

sleekxmpp/plugins/__init__.py

@@ -9,3 +9,5 @@ __all__ = ['xep_0004', 'xep_0009', 'xep_0012', 'xep_0030', 'xep_0033',
            'xep_0045', 'xep_0050', 'xep_0060', 'xep_0066', 'xep_0082',
            'xep_0085', 'xep_0086', 'xep_0092', 'xep_0128', 'xep_0199',
            'xep_0203', 'xep_0224', 'xep_0249', 'gmail_notify']
+
+# Don't automatically load xep_0078