Add Scottish colour and scotland service to fonts

[jimjohnsonrollings]

Resolves #2121

Overall change:
Adds the 'scotland' service to font-families, and the dark saltire colour.

Code changes:

• Add the 'scotland' service to font-families
• Add the 'dark saltire' colour
• Update colour unit test

---

• I have assigned myself to this PR and the corresponding issues
• Automated (jest and/or cypress) tests added (for new features) or updated (for existing features)
• This PR requires manual testing

[sareh]

Looks great so far. You'll want to update the package version in the packages/utilities/psammead-styles/package.json and package-lock.json and add a new row at the top of the CHANGELOG.md file. It will be a minor increase since you're adding new exports, but the package as a whole has backward compatibility. (Right now, version 2.3.0)

[sareh]

👍 Looks great.

The reason Code Climate is erroring, even though you have added a test for the colour being added, is that none of the unit tests for colours.js are currently sufficient. I have opened an issue here to fix the colours unit tests: #2140 . I think that this PR should not need to wait until that is done to be merged in.

[staylos92]

Happy for this to be merged 👍