Update test environment and doc.

- [x] Bump `rails_i18n` from 0.7.3 to 4.0.1 (dunno why it never been bumped?)
- [x] Bump dev dependencies and move them to gemspec.
- [x] Removed 2 year old capybara connection hack and re-introduced
`database_cleaner`.
- [x] Update spec syntax.
- [x] Update README.
- [x] Use `.add_routes`
- [x] Add badges for [Travis](https://travis-ci.org/spree/spree_i18n) and [Code Climate](https://codeclimate.com/github/spree/spree_i18n).

@radar @huoxito @jdutil ping! :penguin: Would be swell if you guys setup Travis for this ;) README link pointed to old Globalize3, also add so contribution link to correct [localeapp translations](http://www.localeapp.com/projects/4605) for this (ppl still tend to push locale changes as commits). Added Poltergeist but it fails on one test, but not with Selenium, maybe it dislike `sleep 1` for change_locale helper.