Calculate progress after saving to prevent lost update

the progress calculation uses County.townlands.all().aggregate which
looks at the database, if the townlands haven't been saved, then it will
look at the old townlands, and hence the progress for today won't be up
to date.

This just happened today.
show more decimal places, otherwise 99.98 looks like 100
Don't show 20 decimal places. it looks ugly and isn't helpful
If there is >1 progress in a day, use the most recent one (which is based on higher id)

I'm reimporting the data now, to fix the bug, so there'll be 2 Progress
for today, but we don't want to use the older (incorrect) one.