test(rest-api): test error handling, HttpMessageNotReadableException
test(rest-api): refactor urls
test(rest-api): refactor response expectations
test(rest-api): refactor request headers
test(rest-api): test error handling, JsonMappingException
test(rest-api): move common integration test stuff to base class
refactor(controllers): use @RestController instead of @Controller

Remove @ResponseBody.