Bump capybara to 2.1.0

Allows us to test for hidden elements properly.

We're using ruby 1.9.3 now so the restriction no longer applies.
Update markup for landing page to be consistent.
Update copy for landing page.
Refactoring landing page HTML
Revert body_classes tag to short form
Merge pull request #35 from alphagov/fix_landing_page

Fix landing page.