WebDAV: Setup CardDAV support

First, TElWebDAVServer.CardDAVOptions.UseCardDAV property should be set to true. ACL support should be also implemented.

Then you should implement the following event handlers of TElCardDAVOptions object, contained in TElWebDAVServer.CardDAVOptions property:

OnCheckUIDUniqueness - each VCard stored on a server should have unique UID. The event handler is used to check if the newly stored VCard has unique UID value;
OnSetAsAddressBook - the event handler should mark the created collection as an address book collection;
OnCheckIfAddressBook - the event handler should check if the collection is an address book.