Tweaks to styles repo page

Commits are fairly self-explanatory.

Re `s` argument in the URL. I think I have mentioned this in some post before, but the point of this is so we can easily link people to the correct styles in the repository. I know that we could link to the source, but it's much more convenient for the user if he can preview the style and maybe even automatically install it instead of looking at the source.

This will probably not work out of the box with the current styles-repo setup on zotero.org, since I see that there are some rewrite rules going on to access styles.php from zotero.org/styles directly. It also looks like the current rewrite rules would not allow arguments at all. So I'm not sure if this is a good enough solution for the production server. Would love to have this implemented, so let me know if I can fix anything on this side.