Just a small visual cleanup because I happened to click on item trades
today! We don't need to repeat "This Week" a million times. Just output
it for the first row, then hide it for the following. (We still include
it in screen reader output for semantic clarity; this is just a visual
cleanup.)
No more of this loading everything into `application.css`! I'm
arbitrarily starting here because that's where I've been playing
lately, but this is part of a larger effort to move toward a more
straightforward CSS architecture (and away from Sass even?)
