Bug fixes and improvements for PropertyIndex discovered during refs #319, mainly contributing to refs #314

* Start index 10 instead 0 for CValueObject (easier to detect bugs)
* Fixed wrong indexes
* Asserts in CPropertyIndex
* Used Icon instead of QPixpmap with indexes, icons are sortable and have a tooltip
* Removed redundant toQVariant methods

src/blackmisc/geolatitude.h

@@ -45,9 +45,6 @@ namespace BlackMisc
             //! Init by double value
             CLatitude(double value, const BlackMisc::PhysicalQuantities::CAngleUnit &unit) : CEarthAngle(value, unit) {}
 
-            //! \copydoc CValueObject::toQVariant
-            virtual QVariant toQVariant() const override { return QVariant::fromValue(*this); }
-
             //! Virtual destructor
             virtual ~CLatitude() {}
         };