Start aligning Admin app with config styles used elsewhere

- no config overrides - now all set in environment
- use different files for staging and live too allow for differently named env variables
- updates to run_app and run_tests scripts to set correct environment (test/development) so correct config picked up
- use environment file on deployed environments to pick correct config

scripts/run_app.sh

@@ -1,3 +1,4 @@
 #!/bin/bash
 
+export NOTIFY_ADMIN_ENVIRONMENT='config.Development'
 python3 app.py runserver