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/avcallsignlist.h

@@ -33,9 +33,12 @@ namespace BlackMisc
             //! Construct from a base class object.
             CCallsignList(const CSequence<CCallsign> &other);
 
-            //! 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();