Move SASS from prototype

- The prototype SASS has changed since it was initially imported
- Also makes sense to split it up a bit while moving it
Migrate latest changes from the prototype

As of today we will be abandonning the prototype

This commit brings in all the changes that have been made since work started
on the app, including:
- Breadcrumbs
- Interface copy
- Stripping out the 'G-Cloud 6' header
Create a temporary folder to process CSS
Add production task to Grunt
Use latest version of Node SASS, clean up package.json
Merge pull request #4 from alphagov/migrate-prototype-frontend

Migrate prototype frontend