replace melange resource by gemoc resource

In order to be independent of Melange when we don't need it and in connection with #8
we need a way to clone/convert the emf resource as Melange does with request such as melange:platform:foo?lang=myLang

we could recreate an equivalent resource converter directly in GEMOC so this feature is available for all gemoc projects without dependency to melange.

It would use uri such as gemoc:platform:foo.xmi?dsl=mylang

This resource would support only the clone/convert and not the adapter (?mt= ) (which would require to get more stuffs from Melange such as the modeltype and adapter java code generation)