Filter: update counts if dives added / removed

Update the filter counts if dives were added removed by the
undo commands. The undo commands call into the filter model
at the right time so that hidden_by_filter is already set.
The filter model keeps track of the counts and emits a signal,
which is caught by the widget.

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

desktop-widgets/filterwidget2.h

@@ -29,6 +29,7 @@ public slots:
 	void updateLogged(int value);
 private slots:
 	void temperatureChanged();
+	void countsChanged();
 
 private:
 	Ui::FilterWidget2 ui;