Scheduling was disabled unintentionally with the config migration in
commit 2ecbfec8.

Annotations are added as a replacement for <task:annotation-driven />.

API v3:
* Media type: application/vnd.de.thm.arsnova.v3+json
* Serializes date as strings conforming to ISO 8601.

API v2:
* Media type: application/vnd.de.thm.arsnova.v2+json
* Serializes dates as timestamps including nanoseconds.

An indentation setting has been added: `api.indent-response-body:false`.