Use setTimeout instead of setInterval

@sheelc and @vito suggested this would be better because setInterval can
possibly run at the same time as itself and that would (potentially) be
all kinds of bad.
Render a different gradient for each hour of the day

Gradients cribbed from dribble http://dribbble.com/shots/889189-Gradients-Time/attachments/96560

Tip of the hat to @sheelc and @vito for basically writing all of this while
I explained how to use my bizarro version of emacs and complained that the
implementation wasn't performant enough and that window.setInterval is so
much superior to a recursive window.setTimeout.

Turns out I was wrong, OS X tends to reduce performance of applications
when running on a low battery, so it just *seemed* to be worse than how
we used setInterval before. My apologies, @sheelc.