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/configurators/ssh_configurator.cpp

@@ -12,7 +12,7 @@
 #include <qtimer.h>
 
 #include "core/server_defs.h"
-#include "utils.h"
+#include "utilities.h"
 
 using namespace QSsh;
 
@@ -59,7 +59,7 @@ void SshConfigurator::openSshTerminal(const ServerCredentials &credentials)
 {
 #ifndef Q_OS_IOS
     QProcess *p = new QProcess();
-    p->setReadChannelMode(QProcess::SeparateChannels);
+    p->setProcessChannelMode(QProcess::SeparateChannels);
 
 #ifdef Q_OS_WIN
     p->setProcessEnvironment(prepareEnv());