Refgenie populater plugin

[nsheff]

We added in 0.11.0 a looper_refgenie_populate plugin, which is awesome.

I think looper_refgenie_populater would also be useful, and might enable using looper for ephemeral compute without even having refgenie configured, and just pointing to a refgenieserver instance...

[nsheff]

This won't be added to refgenconf, but may arise again in the new refgenie1 release.