* 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
* add a GET /accounts/{a}/boostrap URI that delivers the same as GET /
but also mailboxes for a given account, in case the UI remembers the
last used account identifier, to avoid an additional roundtrip
* streamline the use of simpleError()
* add logging of errors at the calling site
* add logging of evictions of Sessions from the cache
* change default Session cache TTL to 5min instead of 30sec
* ensure that all the jmap responses contain the SessionState
* implement missing errors that were marked as TODO
* moved common functions from pkg/jmap and pkg/services/groupware to
pkg/log and pkg/structs to commonalize them across both source trees
* implement error handling for SetError occurences
* Email: replace anonymous map[string]bool for mailbox rights with a
MailboxRights struct, as the keys are well-defined, which allows for
properly documenting them
* introduce ObjectType as an "enum"
* fix JSON marshalling and unmarshalling of EmailBodyStructure
* move the swagger documentation structs from groupware_api.go to
groupware_docs.go
* fix: change verb for /groupware/accounts/*/vacation from POST to PUT
