LPS-35264 Calendar Trash

This is the rebased branch where we implemented the Trash framework into the Calendar.

Three small notes:

1. Currently there's no interface to edit the notification template for event deletion.
2. We also implemented a TrashEntry for declined Calendar Bookings. That way they can be restored as well to the `pending` status.
3. Calendar bookings' TrashEntries are put into the relevant group for that particular resource. In fact:
    * bookings belonging to a user resource, are moved into the personal site of that particular user;
    * in a group resource they are moved in that particular group;
    * the easiest case is for local resources where a real `groupId` is provided.

There's no better way to do this, as far as we know. But at the same time it could be confusing. We suggest to include a small notification which says something similar to:

> The calendar booking has been moved to the trash. **Go to the trash** (link)

Ping @fabiopezzutto and @Ithildir for eventual support.