[xbmc] Add gotham-python-monitor-onclean.diff.

Adds onClean{Started,Finished} callbacks to the Python API.
Backports my XBMC pull request 4877 for Helix.

This is needed for my rewrite of upstart-xbmc-bridge.py as a XBMC add-on (I prefer these callbacks to be added instead of the generic `onNotification` as it makes the code more consistent; also, Helix is probably going to have this).

Note: not tested as I don't have a Gotham development environment, also my XBian is running Helix. I tested the same patch for Helix though.