Allow pages to handle locale and RTL

- Add ability for locale to define a right to left page
- Set the appropriate `lang` on pages
- Set a `direction` class on pages so RTL content can be styled
  appropriately
Use accessors for better encapsulation
Merge pull request #8 from alphagov/rtl-page

Allow pages to handle locale and RTL
Prototype contract testing

we ask the `govuk-content-schemas` for a list of frontend schemas and
then iterate over them running the controller tests for each format.
Add rake task

usage SCHEMA_PATH=/path/to/govuk-content-schemas bundle exec rake test:contract