New dive planning screenshot with 6m stop in it

Signed-off-by: Miika Turkia <miika.turkia@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Documentation: update reference to 6m stop in dive planner

Thanks to Miika we have an updated screenshot

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Fix DM4 dive time

DM4 stores the divetime in local time. The conversion from seconds since
year 1 was 2 hours off. (So there is no timezones involved, which is
good for us!)

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