Consolidate document filter styling

The problem this is fixing is that the stats announcement filter layout was not behaving responsively, whereas the other filter layouts were.

I figured that the reason this bug could be there in the first place was because the two filters, although looking the same, were using different styling.

This PR consolidates the markup / styling of both, hopefully removing any discrepancy between the two. While I was there I also cleaned out some superfluous noise in the markup.

Related bug: https://www.pivotaltracker.com/story/show/73608296