using hashes to perform comparisons between blackmisc value objects stored inside of QVariant

refs #81

src/blackmisc/aviotransponder.h

@@ -331,6 +331,12 @@ namespace BlackMisc
                 return CTransponder::tryGetTransponder(o_transponder, "Transponder", transponderCode, mode);
             }
 
+            /*!
+             * \brief Value hash
+             * \return
+             */
+            virtual uint getValueHash() const;
+
             /*!
              * \brief Register metadata of unit and quantity
              */