add the possibility to easily add a melange file/melange nature to an Ecore project

[dvojtise]

It would be useful, to be able to quickly add the melange nature (and dependencies) to an EMF project with a given ecore file. (via a "Configure" action on the project)
This project can then automatically add an "external language" in the melange file so it will generate the model type classes but will directly reuse the ecore generated java classes as the "Melange Language Runtime"

[dvojtise]

note that I've already tried that this configuration correctly works, the only point is that one have to manually do all the changes (add dependencies, modify .project file, add the melange file with the correct content, launch the generate all on the melange file, ...)