Undo: implement undo of dive site notes editing

Simply copy the code of description editing.

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

desktop-widgets/command_divesite.h

@@ -67,6 +67,18 @@ private:
 	QString value; // Value to be set
 };
 
+class EditDiveSiteNotes : public Base {
+public:
+	EditDiveSiteNotes(dive_site *ds, const QString &notes);
+private:
+	bool workToBeDone() override;
+	void undo() override;
+	void redo() override;
+
+	dive_site *ds;
+	QString value; // Value to be set
+};
+
 } // namespace Command
 
 #endif // COMMAND_DIVESITE_H