Portlet/Form never really submits data due to Content-Type problem

Because of this: https://github.com/instaclick/portlet/blob/master/src/Form.js#L107 , form never really submits data (it gets considered as text/plain).
Solution is to enforce a new request type called "form" (inside of Bisna/HttpRequest) and ensure the requestType is properly converted to "application/x-www-form-urlencoded; charset=utf-8".
Finally, update the Portlet/Form to always send the "form" requestType instead of rely on enctype.