Default some graphs to false

These values are treated as false upon starting Subsurface. Thus they
should be set to false as well. Otherwise extra graphs are drawn to the
profile when exiting the preferences dialog.

Fixes #783

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