Release 6.22.0: Parameter to specify the folder tree for the CardDAV interface

[changerequest]

To configure the folder ID that is used by the CardDAV interface, a new configuration parameter is introduced. At a later stage, users may select/deselect folders inside this tree on their own to control the synchronized folders.

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