Release 6.22.0: Parameter to specify the exposed resource collections in the CardDAV interface

[changerequest]

Depending on the used CardDAV clients, it might be useful to control which collections are exposed via the CardDAV interface. Possible values are '0', '1' and '2'. A value of '1' makes each visible folder available as a resource collection, while '2' only exposes an aggregated collection containing all contact resources from all visible folders. The default value '0' exposes both an aggregated collection, as well as individual collections for each folder.

The file 'contact.properties' is therefore enhanced by property named com.openexchange.carddav.exposedCollections with its default set to 0.