Added Changelog page

The data is fetched (via Ajax) from Picard's repo:
https://raw.githubusercontent.com/musicbrainz/picard/master/NEWS.txt
So we never have to bother updating the page on the site.

The original file contains references to Picard issues which have been
replaced with their URLs. I got the idea from MB-Devel IRC bot which
does the same thing.

The less file behind the changelog page is a bit hacky.
Some less files have also been moved to a 'pages' folder.
Added Changelog page

The data is fetched (via Ajax) from Picard's repo:
https://raw.githubusercontent.com/musicbrainz/picard/master/NEWS.txt
So we never have to bother updating the page on the site.

The original file contains references to Picard issues which have been
replaced with their URLs. I got the idea from MB-Devel IRC bot which
does the same thing.

The less file behind the changelog page is a bit hacky.
Some less files have also been moved to a 'pages' folder.
Merge branch 'changelog' of https://github.com/musicbrainz/picard-website into changelog
Fixed less files path issue

Previously, only less files present directly in the static/less folder
were being watched. The path has been made recursive, so all files are
detected for changes.
Escaped lines and improved parsing

I don't know how I missed it, but all the new lines in the NEWS file
start with a * (used as a bullet point.) That was enough to separate
them from other lines.

For escaping the text 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, but if we do, I think this
will suffice: https://github.com/mathiasbynens/he