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

This is reliant on this pull request on static getting merged to flip the columns: https://github.com/alphagov/static/pull/507

![20141204-government-case-studies-human-rights-and-democracy-report-2012-case-study-egypt ar](https://cloud.githubusercontent.com/assets/35035/5297456/e266930c-7ba6-11e4-8300-4b7be5794938.png)