refs #292, found during debugging

* const override of toQVariant
* missing getter / setters
* metaTuple
* improved toQString
* CClient::setCapability bug
* Fixed wrong ICAO check

src/blackmisc/avairporticao.h

@@ -70,6 +70,9 @@ namespace BlackMisc
             //! Unify code
             static QString unifyAirportCode(const QString &icaoCode);
 
+            //! Valid ICAO designator
+            static bool isValidIcaoDesignator(const QString &icaoCode);
+
         protected:
             //! \copydoc CValueObject::convertToQString()
             virtual QString convertToQString(bool i18n = false) const override;