Include Stagecraft in all envs, not just dev

Seeing as it doesn't exist yet, it would be nice to use the stub
on preview to demo stuff.
Merge pull request #17 from alphagov/stagecraft-in-all-the-envs

Include Stagecraft in all envs, not just dev
Bump grunt-contrib-jshint from 0.6.4 to 0.7.0
Sort gems into groups

So that we can avoid installing development and test gems
in production.
Merge pull request #18 from alphagov/organise-deps-groups

Organise dependencies into groups
Add repository field to package.json
Add config JSON files for each environment
Merge pull request #19 from alphagov/app-config

Add a config.json file
Update README and package.json
Merge branch 'master' into synchronous-render