Lots of fixes/improvements. Add rotate mode.

- Refrain from keeping the screen on when there's no music (avoid burn-in when the music stops)
- Add a rotate mode which replaces the previous mirroring example. Tap to rotate.
- Reduce jankiness when showing/hiding system ui, especially when user repeatedly opens/closes it.
- Drop the dc and hz/2 datapoints. DC isn't part of the spectrum and hz/2 isn't worth bothering with.
- Fix alignment of the horizontal scroller. It was cutting off part of the bottom pixel.
- Greatly simplify the BitmapScroller(s). Things now render onto a single bitmap. This also
  fixes an issue where there'd sometimes be a black column in the voiceprint due to bad math.
- Tweaks to the voiceprint scroll speed (slower), scale factor (wider bass/mids, skinnier treble),
  and analyzer fall off rate (fall a little slower)