Resolve "Add calendars transfer"

Closes #10 (closed), #11 (closed), #12 (closed), #13 (closed), #14 (closed)

See the design on penpot

Calendars

• Transfer 1 calendar
• Transfer all calendars of user
• Disable if calendar is not installed
• Backend tests
• Frontend implementation
  • Redesign of settings section
  • Calendar list picker
  • Information about calendars (shared, last modified)
  • Confirmation modal update

Other

• Add psalm
• Fix edge cases (users without files, users who never logged in)
• Improve user selection
• Improve performance and reduce amount of requests