Let users create/edit/delete letter templates.
Let them upload a CSV file or send a test against a letter template.
Big assumption at the moment is that addresses only have one line, and
therefore one column in the CSV file.
you can get in with either "manage_templates" or "send_letters"
also improve running of a bunch of tests, by parametrising rather than
looping and by cleaning up some mock imports
also added tests for the various hiding logic points
also added new logged_in_client in conftest - so you dont need to
patch all those stupid API calls for get user and get service
