Sync calendar to the watch

[matejdro]

App should sync all user's calendar events to the watch's timeline.

• When event is added or removed from the phone's calendar, watch should be updated as fast as possible.
• When watch disconnects and then reconnect, all changed events should be synced to the watch upon connecting

User should also be able to select which calendars should be synced.

Depends on #15

It should work somewhat like this:

1. Android native side detects whenever user's calendar changes
2. It transmits that to the Flutter side
3. Flutter merges new events with existing calendar db
4. Flutter transmits any changes to the watch, if necessary

Actions that should be on timeline pins:

• Cancel
• Remove (presumably just hides the event?)
• Mute Calendar

Sub-tasks (WIP in https://github.com/matejdro/mobile-app/tree/calendar):

• Allow user to select / deselect calendars to sync
• Sync calendar to the app's internal database when user presses a button
• Send app's internal database to the watch
• Add support for whole day events
• Sync dynamically when event is added/updated/removed from the calendar
• Properly load calendar list on background sync
• Resync every day to capture new events out of 3 day window.
• Filter out HTML from calendar descriptions
• Add support for multi-day events
• Retry watch sync later if blobdb reports error
• Add Remove and Mute calendar actions
• Add event participation calendar actions
• Code quality: rename constants and enums to camelCase to conform to dart guidelines
• Improve error handling
• Also sync past events
• Document isVisible (if pin is visible) and persistQuickView (if quick view is persisted during event duration) timeline flags do
• Nuke blobdb on the watch whenever watch reconnects and it is unfaithful
• Nuke blobdb on the watch whenever watch user switches watches
• Re-sync calendar after user grants calendar permission
• Re-sync calendar after user selects different calendars
• Increase timeline sync window so the watch still gets future calendar events even when disconnected
• Delete pins before adding new ones to make room for new pins in case of full storage
• Sync older pins first to ensure user gets earliest events first in case of full storage
• Add checkbox to the app to enable/disable sync completely

[matejdro]

Example pins by original Pebble app:

That last part is the email/calendar name

(Thanks to UDXS for the pictures)

[matejdro]

Watch displays 3 days of events into the future.