Sanitize and fix cylinder pressure overview

Sanitize and fix cylinder pressure overview

Doing per-dive cylinder start/end pressures is insane, when we can have
up to eight cylinders.  The cylinder start/end pressure cannot be per
dive, it needs to be per cylinder.

This makes the save format cleaner too, we have all the cylinder data in
just one place.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>