* 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
* JMAP query limit of 0 is synonymous with "no limit", but we actually
want to be able to perform queries without any results, for cases
where we only want to count the total number of objects, and also
because it makes more sense semantically
* introduce query parameter validation checks, in order to only allow
query parameters that are actually supported, which is going to be
useful during development of clients
* adds creating addressbooks, calendars, mailboxes
* adds deleting mailbox, event, identity
* adds modifying an email
* introduce template functions for the Groupware API in templates.go,
and use those in route function implementations whenever possible
* add capability checking for mail, quota, blobs
* adds Changes interface
* adds JmapResponse interface
* jmap: add UpdateContactCard and UpdateCalendarEvent funcs
* use JSON marshalling and unmarshalling into a map for toPatch()
implementations
* add updating ContactCards and CalendarEvents to tests
* add deleting ContactCards and CalendarEvents to tests
* make query response totals work when the value is 0
* tests: use CreateContactCard and CreateCalendarEvent funcs to create
objects in tests instead of using a different JMAP stack that works
with untyped maps
* move ContactCard from jscontact to jmap, as it is actually a JMAP
specification item, but also was causing too many issues with
circular references from jscontact -> jmap
* introduce Foo, Idable, GetRequest, GetResponse, etc... types and
generics
* first attempt at a Foo factory type for Mailboxes, needs to be
expanded to further minimize repetition
* add more specialized template functions to avoid repetition
* introduce ChangesTemplate[T] for *Changes structs
