Added a Changelog page

Which fetches data from the NEWS file in Picard's repo and builds an html version of it.

Live at: http://musicbrainz.github.io/picard-website/changelog.html
I've used a snippet from: http://css-tricks.com/snippets/javascript/htmlentities-for-javascript/
that escapes (albeit very crudely) some html. I don't think we need a full blown [solution](https://github.com/mathiasbynens/he)