Update test environment and doc.

- Bump rails_i18n from 0.7.3 to 4.0.1
- Bump dev dependencies and move them to gemspec.
- Removed 2 year old capybara connection hack and re-introduced
database_cleaner.
- Update spec syntax.
- Update README.
- Use .add_routes
- Add badges for Travis and Code Climate.

Fixes #377
Use Spree 2.3.0.beta
When creating a payment method on the admin area, there's a field that specifies the auto capture method of the payment.

There are three options, and the 'use_app_default' one was not translated.

Fixes #381