models: update DiveComputerModel when core data is reset

To implement undo-semantics, we want a longer-lived dive-computer-model
(currently, it is regenerated when the dialog is opened). Therefore, it
must be reloaded when the core data is reset. Do this like for other
models: listen to the dataReset() signal of DiveListNotifier.

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

qt-models/divecomputermodel.h

@@ -25,6 +25,7 @@ public:
 public
 slots:
 	void remove(const QModelIndex &index);
+	void update();
 
 private:
 	std::vector<device> dcs;