refs #825, utility functions

* allow to prefer color liveries (idea: when no airline is found, a neutral livery looks better)
* pick randomly among equal scores

src/blackmisc/aviation/livery.h

@@ -175,7 +175,7 @@ namespace BlackMisc
 
             //! Score by comparison to another livery 0..100
             //! \remark normally used with liveries preselect by airline ICAO code
-            int calculateScore(const CLivery &otherLivery) const;
+            int calculateScore(const CLivery &otherLivery, bool preferColorLiveries = false) const;
 
             //! Object from JSON
             static CLivery fromDatabaseJson(const QJsonObject &json, const QString &prefix = QString("liv_"));