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...
I plan to tackle support for Lua modules too, hopefully in time for EasyBuild v1.14.0, we can do that reorganisation as a part of that (together with moving the `make_*module*` stuff out of the `easyblock` module)