Change syntax.css to be a documented .less file.
Review Request #7540 — Created July 25, 2015 and submitted
syntax.css was our only CSS file (outside of 3rd-party CSS files) that was still a plain CSS file, which made it hard to clean up generated CSS files from the static directory. It also added a barrier to future improvements. This is now a .less file, and no longer appears to be minified. It's documented, and ready to be extended to style CodeMirror syntax classes.
Checked some diffs and rich text. Looked the same as it did before.