Two-way sync events to/from Google Calendar

[adborden]

As an administrator, I want any changes made to events in the app to appear on Google Calendar and any change made to Google Calendar events to appear in the app, so that I can use a powerful calendar tools like Google Calendar (and anything that integrates with it) to make edits to Census Events.

Not everything will be editable through Google Calendar, e.g. language details. Google Calendar supports incremental synchronization. We should follow their guide in order to implement it.

Acceptance criteria

• [ ] Synchronization tasks happens via a managment command
• [ ] Changes to event properties in the app that are not relevant to Google Calendar will not trigger synchronization
• [ ] The synchronization task is either schedules (e.g. cron) or queued
• [ ] Only one synchronization task can occur at a time and they should not be triggered too frequently

[adborden]

I'm putting this task in here, but it's quite a bit of work and we're not sure if it's really necessary just yet.

[mikeubell]

I think this is a very low priority. I think it would be better to permit events to be updated in the app and then repushed to the calendar. Currently an event can only be pushed once. Maybe keep a version number in census_events and one in census_googleevents so we know if an event has been updated after it was pushed.