This is a super tiny data structure that covers an edit mode, a view
mode, and an unconfigured mode. It's mostly a container so that views
don't have to preserve everything directly.
I move the weight edit view into the validated text entry widget, and I
work on some of the unfortunate logic in the weight blur function. I've
left behind a lot of breadcrumbs for things that still need to be done.
I've created the DaySummary structure and set up a list view to go into
the historical view. One hard-coded date is visible as a placeholder to
start filling things into the day summary.