pep8 ocd

Signed-off-by: Raphael Lullis <raphael@lullis.net>
Improvements to the whole trackable model interface, which allows to have history since the beginning. Also added a new signal to indicate that a new model has been changed by a user. This was needed to have user history of provisioning.

Signed-off-by: Raphael Lullis <raphael@lullis.net>