- added support for json serialization using jsonpickle 

- moved convertToJson to convert module

- removed forced content type setting in __generateResponse that
sets MediaType.TEXT_PLAIN as content type, when response is a string :
it should be set exclusively based on what the caller can accept/ has
asked for, as specified in the docstring for this method

- fixed bug that would mangle routed urls after passing more than once
in __registerRouters : this is visible when running unit tests or any
other situation when a RestResource is recreated with the same
"service"