Switch to item decorations to manage header dividers.
This is much more reliable than encoding it in-data. Only cost comes in
that it forces me to backport yet another component since I still can't
update MDC after over half a year.
Redesign the header component to be more aligned with M3 guidelines.
This includes moving the divider to the top when reasonable, using a
smaller font size, and using a tinted coloration to separate itself
from the list contents.
Split up the settings ui into four categories.
This should reduce the visual load on the user as Auxio continues to
accrue possible configuration options.
Resolves#323.