Because the header bar now defaults to blue instead of red, live
needs to be explicitly set to have a red header bar.
This also updates the config to staging, which used to inherit from the
preview one (and get an orange header) but now inherits from the base
config, and so needs its header colour setting explicitly as well.
- 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
