Switch over to consolidated data-private format

@afeld @kaitlin Mind taking a look? Might be easier to go through the commits one-at-a-time.

Also, @gboone, @konklone, @jackiekazil: The next step after this is to write a script to pull the shared data from 18F/data-private and filter out the private stuff. We could repackage some of this code (especially now that it's getting tested, polished and mature) to produce a data import script for 18F/18f.gsa.gov and 18F/Dashboard; or maybe the existing https://hub.18f.us/api/ JSON interface will suffice?
This can be simplified to `collection.delete key`.