The CLASS:PRIVATE and CLASS:CONFIDENTIAL apply to events shared as well as published ones. This adds
two new custom CLASS values: X-NEXTCLOUD-CLASS-PUBLISHED-PRIVATE and
X-NEXTCLOUD-CLASS-PUBLISHED-CONFIDENTIAL, which work the same as the standard values, but only when
they are published into a public calendar. Therefore, you can set an event to be public (fully
visible) for people who you shared internally the event's calendar, but private when the calendar
is published.
Signed-off-by: Thomas Citharel <tcit@tcit.fr>