Replace webob usage in one more file. Document a TODO that should
be clarified, we should probably be using json_response rather than
Response() here.
Modify the TestMeddleware to not rely on the content_type attribute
being present, while werkzeug.wrappers Response() has it the BaseResponse()
object which is often returned in tests does not have it.
Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>