Guess imperial cylinder sizes on CSV import

This patch uses pre-defined working pressures on cylinders to roughly
calculate the size in liters. Imperial selection is ignored here as we
can use the prefix to detect if the value seems like imperial unit (and
the type of cylinder varies based on location, not divers preference in
unit).

Signed-off-by: Miika Turkia <miika.turkia@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>