Add right to left support to govspeak component

Copy over the right to left additions to the govspeak styling from
whitehall.

Also take the opportunity to remove some of the styling on the govspeak
where the list styles were basically identical but written out twice.

Add an example of right to left govspeak to the component docs.
Merge pull request #506 from alphagov/rtl-govspeak

Add right to left support to govspeak component