- Do not show "hidden" or precompiled templates, users don't know about them.
- Remove the client reference if it is the file name of an uploaded file.
- Format the date for created_at
- Added a test for all the different types of letters.
1) One off templated letter
2) Letter created by a csv upload or job.
3) Uploaded letter
4) Templated letter sent by the API
5) Precompiled letter sent by the API