Update colours to the lastest from brand guidance

Lots of this is just sorting the list alphabetically. However these are
the actuall changes that aren't just hex updates:

- department-for-business-innovation-skills: new slug removing 'and'
- department-for-environment-food-rural-affairs: new slug removing 'and'
- department-for-work-pensions: new slug removing 'and'
- foreign-commonwealth-office: new slug removing 'and'
- hm-treasury: new slug adding 'hm'
- office-of-the-advocate-general-for-scotland: added

These are the departments with new hex values:

- attorney-generals-office
- scotland-office
Merge pull request #35 from alphagov/update-colours

Update colours to the lastest from brand guidance