Remove the red header meaning signed in to admin

> Make the header bar red
>
> Red for admin is a good reckon.

– 286fc308d9 (part of https://github.com/alphagov/notifications-admin/pull/130)

Starting to think it’s not such a good reckon. Users could take a guess
at what it meant, but they often guessed wrong.

However, changing the colour of the header bar _is_ useful for us
internally to see which environment we’re in. So this commit makes three
changes:

1. On live, the header bar is always standard GOV.UK blue

2. On other environments, the header bar is some other colour (local is
   very different, staging and preview are related colours)

3. If an enviroment has a different header colour, it has it even when
   you’re not logged in.

app/templates/admin_template.html

@@ -5,11 +5,9 @@
   <!--[if gt IE 8]><!-->
   <link rel="stylesheet" media="screen" href="{{ asset_url('stylesheets/main.css') }}" />
   <!--<![endif]-->
-  {% if current_user.is_authenticated %}
   <style>
       #global-header-bar { background-color: {{header_colour}} }
   </style>
-  {% endif %}
   <!--[if IE 6]>
   <link rel="stylesheet" media="screen" href="{{ asset_url('stylesheets/main-ie6.css') }}" />
   <![endif]-->

config.py

@@ -81,20 +81,20 @@ class Test(Development):
 
 class Preview(Config):
     HTTP_PROTOCOL = 'https'
-    HEADER_COLOUR = '#F47738'  # $orange
+    HEADER_COLOUR = '#F499BE'  # $baby-pink
     CSV_UPLOAD_BUCKET_NAME = 'preview-notifications-csv-upload'
 
 
 class Staging(Config):
     SHOW_STYLEGUIDE = False
     HTTP_PROTOCOL = 'https'
-    HEADER_COLOUR = '#F47738'  # $orange
+    HEADER_COLOUR = '#6F72AF'  # $mauve
     CSV_UPLOAD_BUCKET_NAME = 'staging-notify-csv-upload'
 
 
 class Live(Config):
     SHOW_STYLEGUIDE = False
-    HEADER_COLOUR = '#B10E1E'  # $red
+    HEADER_COLOUR = '#005EA5'  # $govuk-blue
     HTTP_PROTOCOL = 'https'
     CSV_UPLOAD_BUCKET_NAME = 'live-notifications-csv-upload'