This allows the ODK export functionality to append latest changes
to a single database path, instead of downloading the full database
history which can stretch over many years. This saves a lot of time
for the daily survey job.

The WRSIS survey processor can already limit the download size to
the current season(s) with a start-date parameter.

The Kobotoolbox survey processor doesn't have a solution for
avoiding the daily download of extensive historical data. This needs
investigating further at some point.

This reverts commit d84d1b1e.