converting value objects to/from QVariant

refs #81

src/blackmisc/avaltitude.h

@@ -104,6 +104,15 @@ namespace BlackMisc
                 return MeanSeaLevel == this->m_datum;
             }
 
+            /*!
+             * \brief QVariant, required for DBus QVariant lists
+             * \return
+             */
+            virtual QVariant toQVariant() const
+            {
+                return QVariant::fromValue(*this);
+            }
+
             /*!
              * \brief Get reference datum (MSL or AGL)
              * \return