MDL-36621 calendar: Ical event should display source info
MDL-36621 calendar: Display subscription info in calendar event popups
MDL-36621 calendar: cache calendar subscriptions and showicalsource setting

Now MUC is used to cache subscription information when the constructor for an event is called, which is child of a ical subscription.
A new setting calendar_showicalsource is introduced which controls if the ical source should be displayed along with events in the calendar