We want to set some custom backgrounds for the visualizers, and
those need to track with the current theme. SpThemeManager will
watch the systems theme changes (including dark theme) and
update the loaded CSS resources as necessary.
This gets started on allowing the user to select a region.
Nothing is yet responding to the changes in selection, but
that can come later.
Ideally, we will truncate (or mark rows invisible/insensitive)
if they do not fall within the selected time region.
