Serve govuk-component documentation as JSON

Previously this documentation was stored in the govuk_component_guide app and was
frequently out of sync with static, or failed if pointing at a different static
endpoint.

This moves the documentation into static and exposes it as an API-like endpoint,
so that the documentation data could be auto generated in the future, rather than
a static file.
Merge pull request #439 from alphagov/component-documentation-api

Serve govuk-component documentation as JSON
Update all instances of greys in static to use either semantic
colour variables from the toolkit or nearest toolkit grey

• rationalised corresponding grey
• update to semantic variables
• update grey variables to match toolkit rather than static colours
Remove import refernce to local static colours file

• remove reference
• delete _colours.scss

https://www.agileplannerapp.com/boards/105200/cards/5541
Merge pull request #440 from alphagov/remove-refactor-greys-from-static

Remove and refactor local greys from static
Move report-a-problem related styles to _report-a-problem.scss

This allows apps which rely solely on `header-footer-only.css` to also
get the 'report-a-problem' toggle styles.
Report-a-problem improvements

These changes in markup and styling make the report-a-problem functionality much more
self-contained, thus removing the need for apps to include custom CSS
for displaying the report-a-problem form correctly.

The report-a-problem stylesheets are also refactored to use the latest and greatest from
`govuk_frontend_toolkit`.
Merge pull request #441 from alphagov/report-a-problem-improvements

Report-a-problem improvements
New metadata component markup and Sass