migrated the codebase to Qt6 and fixed some compatibility issues

* used a Qt6 ported version of SortFilterProxyModel
* used an updated Qt6 compatible version of QXZing
* added a flag to windows linker to avoid WinMain problem of MSVCRTD
* renamed utils.cpp to utilities.cpp for avoiding confusion with the same file name in SortFilterProxyModel

client/logger.h

@@ -8,6 +8,8 @@
 #include "loglevel.h"
 
 #include <QString>
+#include <QStringList>
+#include <QIODevice>
 #include <QTextStream>
 
 constexpr const char* LOG_CAPTIVEPORTAL = "captiveportal";