Fix regression in tests and improvements

* Fix regression: Some tests have been omit since https://github.com/apotonick/apotomo/commit/9fda7e5e857d1ba943a252b59aa02375fcbcfaef
* RailsIntegrationTest: Create RoutingTest (moved from ControllerMethodsTest)
* RailsIntegrationTest: Add assertions for content type
* RailsIntegrationTest: Add assertions for status code
* Simplify RenderTest
* Style unifying