Classpath for parser Xtend

[fontanella]

Context : In the sample "https://github.com/diverse-project/k3/tree/master/sample/fr.inria.diverse.k3.sample.loadXtendModelFromXtend"

The parser has some inputs arguments among the classpath. We set the classpath argument to "null" and the parser manages classpath as its own classpath (same dependencies and other output path).

@barais It will be interresting to integrate a funtion loading the classpath of a IProject.