- show the correct gasmix in the profile;
- make gases available for gas switches in the profile after they have
been added;
- persist gas changes;
- add air as a default gas when adding a dive.
This still has problems when undoing a gas switch - instead of
completely removing the gas switch it is just moved to the next point in the
profile.
Signed-off-by: Michael Keller <github@ike.ch>