support for hierarchical module naming schemes

@geimer: this should fix the problem that's blocking you right now

I might need to figure out one more thing w.r.t. the devel module name before this really works for you, I'm looking into that...
done for consistency with `easybuild_mns.py` mainly, but in fact the module naming is not important here (EasyBuild doesn't care about the name of the module in which the class lives, only about the `module_naming_scheme` namespace and the actual class name (and the fact that it should derive from `ModuleNamingScheme`