New metadata component markup and Sass
Add basic test to ensure docs are returned

This test ensures that docs are returned when you try and request them.
As the docs controller tries to parse the JSON it also validates that
the format is correct and will fail if bad JSON is in the docs file.
Add instructions for running static locally

In particular how to have static point at it's own assets, not default to
static.dev.gov.uk, which won't exist unless you're running our whole VM stack.

This makes it easier for:
 - new devs seeing how static works
 - external contributors
 - developers of apps that depend on static (eg, may use slimmer)
Merge pull request #443 from alphagov/metadta-component

New metadata component markup and Sass
Merge pull request #446 from alphagov/how-to-run-locally

Add instructions for running static locally