Redesign validator output

[Klortho]

Copy from http://validator.w3.org/unicorn/check:

• Each phase is marked very clearly, with a banner, that has an expand/collapse control
• The banner also gives the number of info, warning, and error messages. Clicking on one of those controls in the banner causes those messages to be shown
• The messages each have a link to more info -- we need that. Our messages should definitely link to the place in the recommendation document where the issue is described.

Note that this unicorn tool is badly broken in many ways, but the output format is nice!