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.

sat/plugins/plugin_misc_merge_requests.py

@@ -106,8 +106,8 @@ class MergeRequests(object):
         @param name(unicode): name of the handler
         @param handler(object): instance of the handler.
             It must have the following methods, which may all return a Deferred:
-                - check(repository): True if repository can be handled
-                - export(repository): return export data, i.e. the patches
+                - check(repository)->bool: True if repository can be handled
+                - export(repository)->str: return export data, i.e. the patches
                 - parse(export_data): parse report data and return a list of dict
                                       (1 per patch) with:
                     - title: title of the commit message (first line)