Prepare the Integration with systemd

This is an intermediate commit providing
basic functionnalities for setting up
integration of the framework with systemd.

 - file afm-unit.conf is a mustache template
 - translation of config.xml to json object
 - mustache (extended) application of the json to the template
 - post processing of the result for extracting unit files

This processing is currently available as a test
(and a tool) and will be integrated after more
developement, test and validation.

Signed-off-by: José Bollo <jose.bollo@iot.bzh>