Desktop: Fix Gas Editing for Manually Added Dives.

- 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>

commands/command.h

@@ -100,6 +100,7 @@ enum class EditProfileType {
 	ADD,
 	REMOVE,
 	MOVE,
+	EDIT,
 };
 void replanDive(dive *d); // dive computer(s) and cylinder(s) of first argument will be consumed!
 void editProfile(const dive *d, int dcNr, EditProfileType type, int count);