Keep on chomping

This change makes significant changes to chomp. It is rebased with the changes from https://github.com/InsolvencyService/rps-alpha/pull/44 and therefore should be merged afterwards.

- Puts it in the overall application folder.
- Separates the XML generator into its own module.
- Introduces unit test generators which test the mapping of json attributes to xpath locations.
- Introduces a very basic acceptance test pulling data from the database.

The integration with the database is a little hacked in, but that area is in a pretty raw state anyhow. I added a method to the SQLAlchemy object to help it serialise, which is unlikely to stand the test of time.