[Caldav] Multi-account configuration

Configuration
13

I’ve posted my answer on the PR!

For information, we are debating the type of sharing:

  1. Either we share a calendar with the entire instance (shared calendar mode: yes/no)
  2. Or we offer to share a calendar only with certain people in the instance

Both options are possible, but option 2 is still more complex at many levels (what happens with scenes?)

See my 2 messages on Github