Arguments passed/retrieved to/from LunaService must be stringify/parsed

Due to the internal implementation of the LunaService component it's currently required to
stringify/parse the JSON arguments when calling a service method or retrieving a response.

Signed-off-by: Simon Busch <morphis@gravedo.de>
Merge pull request #3 from webOS-ports/morphis/work

Arguments passed/retrieved to/from LunaService must be stringify/parsed