Cleanup stray whitespace and tabs
Move navbar styles into a separate stylesheet
Simplify publisher navigation bar

* Make the design more like Bootstrap 3, flat, starker contrast, simpler
* Give the navigation bar black borders, one of these will be used to
indicate environment
* Remove the divider
* Remove the background colour on active links
* Increase the body’s padding to account for the larger navbar
Add environment colours and apply to nav border

* Use LESS variables for the different environments
* Use an environment- class to switch environments
  * eg on `body` or `html`
Add an environment message

* Background colour based on environment
* Defaults to a dark grey when there is no environment class set
Determine environment

* Use Plek.current.website_root to determine the current environment
(rather than Rails.env or ENV[‘GOVUK_APP_DOMAIN’])
* Create an environment_name helper for the message and class
Only apply navbar styles to navbar in header

* There are fixed footer navbars in publisher
Default to development environment
Include environment based favicon
Configure environment name at deploy time.

Instead of trying to work it out from the website_root, configure it at
deploy time.

This uses a GovukAdminTemplate module to hold the config in anticipation
of this functionality moving into the gem.
Merge pull request #203 from alphagov/distinguish-environment

Distinguish between Publisher environments