Avoid Javascript Caching of editor CSS

The CSS path indicated for the HTML in the editor window is attached by javascript. Javascript caches all URLs/Pathes so this CSS is also violently cached by the browser, which created very significant problems for themers - once they indicate custom CSS file, and start editing it, all edits after the first one are ignored, until you clear browser cache or restart browser. It almost makes the feature unusable.

Attached patch adds ?nocache=[timestamp] at the end of the CSS file path to avoid caching (it's obviously not a performance issue since content edit screen is not a performance-sensitive page, anyway).