Added cache busting to assets URLs

* Added Symfony "framework/templating/assets_*" Configuration  setting
* Added a URL rewriting rule to our dev Nginx server : "/assets/%assets-version%/" URLs are converted to un-prefixed URLs
Removed "AsseticBundle"
Books assets URLs are now relative
Merge pull request #2 from DrBenton/assets-cache-busting

Assets cache busting, Assetic removal