jp: jp asyncio port:

/!\ this commit is huge. Jp is temporarily not working with `dbus` bridge /!\

This patch implements the port of jp to asyncio, so it is now correctly using the bridge
asynchronously, and it can be used with bridges like `pb`. This also simplify the code,
notably for things which were previously implemented with many callbacks (like pagination
with RSM).

During the process, some behaviours have been modified/fixed, in jp and backends, check
diff for details.

twisted/plugins/sat_plugin.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 # SAT: a jabber client