CylindersModel: use flag to decide whether we are in planner

On desktop, we have two CylindersModel concurrently: One in the
planner and one on the equipment-tab. They act differently, because
the former modifies displayed_dive directly, the latter issues
undo commands.

To differentiate, we used the in_planner() function. However, that
appears extremely brittle, especially when combined with undo-commands.
Therefore when generating the model, pass in a parameter that says
whether this is for the planner or the equipment tab and use
that flag to decide how to act.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

qt-models/diveplannermodel.cpp

@@ -415,6 +415,7 @@ int DivePlannerPointsModel::rowCount(const QModelIndex&) const
 }
 
 DivePlannerPointsModel::DivePlannerPointsModel(QObject *parent) : QAbstractTableModel(parent),
+	cylinders(true),
 	mode(NOTHING),
 	recalc(false)
 {