Apple Calendar Support Stabilize

[yujonglee]

Things to sort out:

• Ignore event hide/unhide upcoming events #960
  • Ignore single event, or recurring event
  • Rule-based event filtering

apple calendar import creates multiples of far off future meetings. Ignore event is inconsistent (ignored events will reappear) after restarting the app here too.
#2853 (comment)

• Unsure about current events.json and calendars.json format.
  • Done. Will use json

TODO