Group common scripts

[joshbetz]

Concat can be a little overzealous in cases where a script or style is enqueued conditionally. Say a script is used on one page. Ideally we wouldn't serve a different Javascript bundle on that page that is the same as every other page with the one extra script added. The bundle that loads on every other page is most likely already cached in the user's browser. We really just need to serve the additional script separately (or maybe inline?).