DONE
Refactor Notification class. Create a function get_item_last_revisions(). Notification class has methods for getting the content, meta diff, generate the url to the UI diff on moin, a method for rendering templates and the signal receiver function. Create tests for the function get_item_last_revisions() and for get_content_diff(). Tested manually the functionality for different actions.
The problem arises with the deleted item, because we can't get the subscribers list for a NonExistent item.
I am sorry for editing the calendar entry one day after. Yesterday moin server was unavailable for a period of time.