Cleanup the locale keys.

All locales already exists in spree_i18n so maintenance of diffenent
locales in this module also is not very DRY.
Cleanup migrations.
Update specs to use Capybara 2.

- Cleanup the specs.
- Add coverage reports.
- Capybara 2 changes.
- Fuubar make spec runs nice :)
- Add locale spec.
Updated license date.
Some code cleanup.
Updated Travis config.
Updated readme.