Planner: clean up the function that tracks our gases

This doesn't add gases. It just makes sure they are there.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Planner: only update the plan after the cylinder data has been updated

This way we avoid trying to create a dive from the plan while the plan
references the cylinder that has just been changed.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>