* in the JMAP API as well as in several places in the Groupware
framework, use a single jmap.Response[T] object to return the
payload, the language, the session state and the etag/state instead
of individual multi-valued return values
* add Groupware APIs for creating and deleting addressbooks
* add Groupware APIs for creating and deleting calendars
* add JMAP APIs for creating and deleting addressbooks, calendars
* add JMAP APIs to retrieve Principals
* fix API tagging
* move addressbook JMAP APIs into its own file
* move addressbook Groupware APIs into its own file
