Add in helper for checking for development environment

- Create helper for development environment check
- Don’t worry about applying the file digest to files whilst on
development, just pull from the base files.
- Remove extra margin around the <pre> elements.
Use Rails.env for environment checking instead
Gah! Rails.env.development? is a much better choice.
Merge pull request #17 from rehttp/dont-use-file-digests-in-dev

Add in helper for checking for development environment