Move function to proper place

Instead of writing TODO comment blocks, just do the work, and move the
function to the proper class. Further, after review from Berthold, cleanup
the function. There is no reason that getGasList() is member of
any class. It is just a non-class helper, and as it is only used
here, a static helper.

Signed-off-by: Jan Mulder <jlmulder@xs4all.nl>

qt-models/diveplannermodel.h

@@ -52,7 +52,6 @@ public:
 	divedatapoint at(int row);
 	int size();
 	struct diveplan &getDiveplan();
-	QStringList &getGasList();
 	int lastEnteredPoint();
 	void removeDeco();
 	static bool addingDeco;