Add civil_service org type and allowed_promotional

So that promotional homepages can be used by more than just executive
offices.
Allow all promotional orgs to set promotions
Let promotional orgs have promotional template
Update styles for promotional show page

- Only colour DPM and PM pages fuschia
- Float normal organisation headers next to top links
- Show organisation about text if no promoted policies
Add i18n strings for Civil Service
Add civil-service brand colour

- Update the toolkit for the new brand colour
- Update the colours file to have the new brand colour
- Update the Sass on the organisation page to use the new brand colour
  for links and background images
Improve readability of allowed_promotional_keys method
Merge pull request #1413 from alphagov/civil-service-org

Add the ability to add Civil Service organisation type

https://www.pivotaltracker.com/story/show/66653054