Renamed main module to remove underscore.

Changed server to hook into requests lib detection of non 2xx response codes.

Added error handler for 404 and 500 (maybe add more?).

Changed submodule for govuk_templates as main module changed name. This may go altogether soon.

Added a couple of tests.
Merge from master
Fix price paid test amount
Force remove old git submodule name
Merge pull request #18 from LandRegistry/refactor-cleanup

Refactor cleanup