Automated conda packaging of openmm-dev [ready to merge]

This is a (potentially doomed) initial attempt at automated conda packaging of openmm-dev.
Good catch!  This was what @kyleabeauchamp had in [`repex`](https://github.com/choderalab/repex/blob/master/.travis.yml#L8) which I think came from [`mdtraj`](https://github.com/rmcgibbo/mdtraj/blob/master/.travis.yml#L8).  I can switch this back to `clang++`.