- added automatic handling of 501 NotImplemented error in case a url
exists but the specific requested method does not .
For simplicity, this is done via an added dict called "urlMethods" in
RequestRouter, that maps urls to lists of implemented http methods , and
is filled in_registerRouters

- 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"

bug fixes: handle conversions of numerics in JSON responses, better parsing of arguments with unexpected characters