Load minified JS and CSS

[DJPaul]

Trunk now has a minified version of each JS and CSS file which is automatically generated. We need to update everywhere we load any JS and CSS file, and optionally decide to load in the minified version over the non-minified version. Note that the minified version only exists in the build release, so we'll need to check the file exists.

[djpaul]

In 8772:

Core: make sure we load minified JS and CSS when SCRIPT_DEBUG is set.

Fixes #5615