Dim zeros in deck picker, second try

Again, this shows zeros in the deck picker in a rather light gray, the way Anki desktop does it. Like this decks where you actually should do some reviews stand out from the decks where you are through for the day.

This one, unlike #323, <em>un</em>dims counts when they go from zero to bigger numbers. (Oops.)

I also renamed a few colors to a) use names that describe what happens, rather then how it looks, and b) avoid the ambiguity of `red` = `#990000` (AnkiDroid, before) and `red` = `#ff0000` (everywhere else).

As usual, i did some whitespace clean up and put that in an extra commit.