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/valueobject.h

@@ -163,7 +163,7 @@ namespace BlackMisc
         //! Base class enums
         enum ColumnIndex
         {
-            IndexPixmap,
+            IndexPixmap = 10, // manually set to avoid circular dependencies
             IndexIcon,
             IndexString
         };