Chomp API

This API is for the Leenatron to get documents for processing in CHAMP.

Still to do:
  - Fill in all of the variables in the XML templates
  - Implement the /chomp/id/ endpoint (it's not strictly required for leenatron)
  - Add the ability to put chomp claims in a failed state

I'm merging now because we want to test out the Leenatron