provide an easier way to read a configuration file

[samthiriot]

It is now (after some refactoring already - before the expected class was expected !:

new GenstarJsonUtil().unmarchalConfigurationFileFromGenstarJson(
					 Paths.get("src/test/resources/rouen_demographics/rouen_demographics.gns"));

we might expect instead a GenstarConfigurationFile.loadFromJson(...) which would not require the user to discover the concept of a class, create an instance, and "unmarshall"

[samthiriot]

same for writing a configuration file:
try { new GenstarJsonUtil().marshalToGenstarJson(relativePath.resolve(CONF_EXPORT), gcf, false); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); }

is not the easiest way for a user to just to a "saveToFile"!