Update environment configs to override blue header

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.

config_live.py

@@ -14,3 +14,4 @@ class Live(Config):
     DESKPRO_API_KEY = os.environ['LIVE_DESKPRO_API_KEY']
     DESKPRO_DEPT_ID = os.environ['LIVE_DESKPRO_DEPT_ID']
     DESKPRO_ASSIGNED_AGENT_TEAM_ID = os.environ['LIVE_DESKPRO_ASSIGNED_AGENT_TEAM_ID']
+    HEADER_COLOUR = '#B10E1E'  # $red

config_staging.py

@@ -13,3 +13,4 @@ class Staging(Config):
     DESKPRO_API_KEY = os.environ['STAGING_DESKPRO_API_KEY']
     DESKPRO_DEPT_ID = os.environ['STAGING_DESKPRO_DEPT_ID']
     DESKPRO_ASSIGNED_AGENT_TEAM_ID = os.environ['STAGING_DESKPRO_ASSIGNED_AGENT_TEAM_ID']
+    HEADER_COLOUR = '#F47738'  # $orange