refs #314, fromQVariant / location of toQVariant

* renamed fromQVariant to convertFromQVariant, the "from" methods imply the object is changed (fromJson, fromString ..)
* implemented fromQVariant - changing the object by QVariant
* moved toQVariant into PQ template
* free function setFromQVariant

src/blackmisc/statusmessagelist.h

@@ -38,12 +38,14 @@ namespace BlackMisc
         //! Find by severity
         CStatusMessageList findBySeverity(CStatusMessage::StatusSeverity severity) const;
 
-        //! \copydoc CValueObject::asQVariant
+        //! \copydoc CValueObject::toQVariant
         virtual QVariant toQVariant() const override { return QVariant::fromValue(*this); }
 
+        //! \copydoc CValueObject::fromQVariant
+        virtual void fromQVariant(const QVariant &variant) override { BlackMisc::setFromQVariant(this, variant); }
+
         //! Register metadata of unit and quantity
         static void registerMetadata();
-
     };
 }