Dependencies of OpenGEM components

With the ongoing work on the NHE and the split of NRML artifacts into a separate repository (from the OpenQuake repo), we've discussed possibilities for separating and organizing the various components.

Here is a simple diagram explaining a possible component break-out, as well as a dependency graph: https://docs.google.com/a/openquake.org/drawings/d/1GvPMbEExwL1wgCURWRZyTC8fyRRVBWOD80THc16pdZw/edit?hl=en_US