Rewrite as a MailExtension

[kewisch]

Thunderbird now focuses on (MailExtensions)[https://developer.thunderbird.net/add-ons/mailextensions] for extension development. I'm rewriting this extension as a MailExtension, and at the same time building a MailExtensions API for calendaring. I'm not including all the done items, but here is whats left to do as of filing this bug.

UI

• [x] Event dialog - move UI into frame MVP
• [ ] Event dialog - validate reminders
• [x] New Calendar Dialog - make calendar creation pretty MVP
• [x] Port Options UI abc3a417dcf7b6940f599140523f216eca846af4 MVP
• [x] Make sure #11 has not regressed

Items

• [x] Use of RFC3339 for LASTACK and SNOOZE-TIME MVP
• [x] Ensure timezones work, our ical.js doesn't have a timezones registry MVP
• [x] Organizer part of attendees or not
• [x] Pref for disabling attendees
• [x] Figure out if we can throw in parseEventStream
• [x] deal with events that have DURATION instead of DTEND
• [x] Support HTML descriptions (and port 6625aba20513a6f579261789ae8929e086328637) MVP

Calendars

• [x] Throttling of requests
• [x] Avoid hitting rate limiting (#187)
• [x] Conflict resolution MVP
• [x] Deal with invitations and importing events MVP
• [x] Disabling calendars on certain errors
• [x] Ensure that network failures will trigger offline mode (see #163) MVP

Experiment

• [ ] Event dialog - API to deal with user changes. Frame should be able to react to that
• [ ] Create capabilities for UI, e.g. disabling attachments, attendees, privacy, etc
• [ ] Event dialog - ability to validate the event, extension should be able to say when something is wrong
• [ ] Reminder dialog - Provide some capabilities?
• [x] Properties dialog - Capability to force readonly mode, don't allow changing in the calendar properties dialog
• [x] Properties dialog - Capabilities w.r.t. refreshInterval. Minimum value? Provide list of values? Maximum value?
• [ ] Properties dialog - add an extension frame
• [x] Addon calendar wizard - discuss more future proof way to trigger creation
• [ ] Activity Stream API?
• [ ] Validate capability names

Recurrence

• [x] Verify etags for recurring events work MVP

Migration

• [x] Migrating ICS calendars, setting googleCalendarName
• [x] Notification/UI when migratable calendars happen
• [x] Ensure properties such as disabled/color/etc are migrated

[kewisch]

Hey folks. I'm going to go ahead and lock this issue since I want to use it for tracking the rewrite. If you are experiencing any issues please file a separate one.