Correct unit tests and a minor optimisation
@pvuorela, I think the fact to move mKCal to validate notebooks, make the calendarevent test fails now here. Indeed, events were created before without notebook, which is not possible anymore.
The MR is also fixing a warning reported by the test (see testDate one in tst_calendarevent) : deleting two entries in a row was not possible because the memory calendar is emptied after each delete, due to the save action from calendarapi. I'm fixing this like in CalDAV plugin by reloading the event from storage if necessary.
Finally, I propose a micro optimisation in the calendar worker. When loading events, it is looping on all the events in memory. This can be a long list, if the user have moved within months in the calendar. For each event in memory it is creating the Event structure from the incidence, and most of the time it is trashing it immediately after because this Event structure was already sent to the calendar manager.