Implement REST service with Akka HTTP

[tdauth]

• https://doc.akka.io/docs/akka-http/current/?language=scala
• https://www.playframework.com/ (maybe to advanced - model view controller, we don't want a web application, only a RESTful service)

Akka HTTP is not a real framework but a suite of libraries. Since we do not provide a web application here but a simple REST interface, it should be sufficient.

TODO instead of using rest.model, map our types from api into JSON and back.

[tdauth]

Drop the REST API for applications, test suites, test cases etc. and replace it by the REST API for the state machines only.
The types in model and dsl should be adapted to the types in api.