* 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
