ical-rs overhaul

[lennart-k]

This PR integrates a complete overhaul of my ical-rs fork.
This new ical-rs version is much stricter in parsing input data but also more aware of it, which is a crucial step towards JSCalendar support.

Breaking changes:

• The new implementation would fail at parsing invalid objects already inserted into a calendar.
  • State breaking change in release notes
  • Perform healthcheck on startup to let users know something's going wrong
  • Hence, the release from this PR MUST be reversible in case issues arise.

Logic outsourced to the ical-rs library:

• Recurrence expansion
• Birthday/Anniversary event generation
• Parsing calendar objects
• date,date-time,timezone-related data types
• Expanding imported calendars into calendar objects
• Merging calendar objects into calendar exports

Todos:

• Remove todo!()
• Make object_id extrinsic
• Remove object_id from ETag
• Fix calendar-query compfilter
• Strategy to deal with invalid objects when updating (Option to skip them. On startup, broken objects are listed)
• Useful error messages when uploading invalid data

Other improvements:

• Support for proprietary timezone identifiers (looking at Microsoft)
• Less broken implementation of recurrence expansion

Other todos that don't need to be in this PR:

• Unique UID in addressobjects table (This must be in a later version since it's a
• ETag generation
• Implement retrieval of partial calendar objects with prop filters
• remove wrapper types AddressObject/CalendarObject
• Make sure this is highly performant