Allow returning http errors with exceptions

before:
    def my_response_method(self):
        ...
        if error:
            return template, {'status'=400}

after:
    def my_response_method(self):
        ...
        if error:
            raise MyResponseError("bad thing happened")
where MyResponseError inherits from HTTPException

requirements.txt

@@ -7,3 +7,4 @@ requests
 sure<1.2.4
 xmltodict
 dicttoxml
+werkzeug