Add some more department colours

This includes:
- Northern Ireland
- Leader House of Lords
- Leader House of Commons

The websafe colours are still the original - Mark needs to update these
when he gets time.

Also, the govuk_frontend_toolkit depends on
alphagov/govuk_frontend_toolkit#32 being merged, hence the local reference.
Update Gemfile to published govuk_frontend_toolkit
Add websafe variants of new colours
Merge pull request #281 from alphagov/new-department-colours

Add some more department colours

https://www.pivotaltracker.com/story/show/44964555