Undo: implement undo of dive site location editing

Simply copy the code of note editing. It's a bit more complex,
since we have to parse the Gps coordinates. For consitency,
rename the COORD field to LOCATION (the field in the dive_site
struct is called LOCATION).

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

desktop-widgets/command_divesite.h

@@ -92,6 +92,18 @@ private:
 	QString value; // Value to be set
 };
 
+class EditDiveSiteLocation : public Base {
+public:
+	EditDiveSiteLocation(dive_site *ds, const QString &location);
+private:
+	bool workToBeDone() override;
+	void undo() override;
+	void redo() override;
+
+	dive_site *ds;
+	location_t value; // Value to be set
+};
+
 } // namespace Command
 
 #endif // COMMAND_DIVESITE_H