[Calendar] Enhance import feature

Hi,

The import calendar events feature is a bit raw, FMPOV it would be far better if:

  • it would (optionally) allow to replace already existing events in calendar,
  • at least, tell at the end how many new events were imported, and even better: give the list of those imported events

(based on my current experience while importing ICS files generated by Calendarscope).

What do you think?