Make concurrent modification detection on Qt containers optional

[omix]

QtJambi's iterators do a container modification check on each next()/hasHext().

QStringList stringlist = ...
for(String s : stringlist){
    stringlist.append("new string");
}
// will throw ConcurrentModificationException

This is time consuming and should be optional only.

[omix]

This feature will be available in QtJambi 6.5.1.

Runtime argument -Dio.qt.enable-concurrent-container-modification-check=true will activate concurrent modification checks during container iteration.