Finding by ownerId depends on a new database view and is NYI.

Default to 'vnd.de.thm.arsnova.v3+json' if no specific content type is
requested via Accept header or path version prefix.

Views are now checked for existence instead of creating them on every
startup.

Decide between 'vote', 'school' and 'abcd' target format based on count
of AnswerOptions.

When null was set as database key, the whole view would be requested
before this change.

Revisions are copied by default but explicitly skipped for
V2ToV3Migration.

Using format caused problems because Jackson does not support multiple
type names being mapped to a single class.

This reverts commit 96b0cf42.

For now, only Answer and AnswerStatistics migrations are tested.

While type works fine for deserialization from CouchDB, it is not part
of the public v3 API. The format property is available in both cases.

A new cache 'room.id-by-shortid' has been introduced to speed up ID
lookups.

Some legacy identifiers remain very persistently.

Additionally, remove obsolete VisitedRoom repository and renamed
VisitedRoom references to RoomHistory.