[master] Cleanup locales.

- Removed no longer used locale key.
- Replaced some keys that exist in spree core.
- Add missing keys.
- Terms view and locales no longer used.
- Add missing pluralization keys.

All tested with i18n spec gem.
[master] Make specs pass.

- Add helper spec.
- Change lambda to expect.
- Set js_errors to false for Poltergeist to make tests pass without
interference from Spree core js issues (you can easy change back to
true).
[master] Fix assets paths for 2.2.0.beta

Also use $(document).on thats more agnostic.
[master] Remove empty helpers and cleanup Gemfile.
[master] Change ready to on page:load for Turbolinks.
[master] Update README and add LICENSE.