This involves some changes to the template block structure to make it
easy to compress the correct files.

* A new block cdn_scripts has been introduced as CDN-loaded scripts
  can't be compressed.
* A new setting 'USE_LESS' controls whether to use the LESS-generated
  files or the compressed files (which will need to be generated
  manually as they aren't in source control).
* A fallback for jQuery UI is added
* The CSS block was renamed to be clearer
* The bootstrap CSS was brought out of the LESS file into the page.
  This makes it easier to compress.