CardDAV and CalDAV support

[chrostino]

Pre-Submission checklist

• [x] There is no existing issue that already asks for this feature.
  
• [ ] The feature already exists in rclone (on your PC or in Termux)
• [ ] I am prepared to help make this feature

What version of Round Sync are you using (About -> App version)?

2.2.2

What problem are you trying to solve?

Being able to sync calendars and contacts also within the same app that syncs my files

What should Round Sync be able to do differently to help with this problem?

Be able to sync calendars and contacts the same way DAVx5 app does

being very hones I don't know if the feature is even possible to implement, in case not just dismiss this issue, but it would be an important feature addition to this app making it possibly the best in its category

[newhinton]

This is simply out of scope.

If you need calendar sync: https://www.davx5.com/