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/namevariantpairlist.h

@@ -36,9 +36,12 @@ namespace BlackMisc
         //! Get name index
         int getNameRowIndex(const QString &name);
 
-        //! CValueObject::toQVariant()
+        //! \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
         static void registerMetadata();