Improve JSONP support (timeout/abort/complete)

The jsonp function did not work together with a timeout, for jsonp the timeout is important since there is no way to determine the call has not returned a successful call without the HTTP status codes.

This commits add support for a jsonp abort function, which gets triggered by the timeout. At the moment the users o.succes function is called directly bypassing the reqwest succes function. The commit calls the reqwest succes function instead, which will cleanup the timeout and also makes sure the complete function is triggered.