UI: Add CreateQThread helper function

Allows creating a QThread via an std::function.  A backward-compatible
alternative to QThread::create for Qt versions older than 5.10 (when it
became available in Qt).

UI/qt-wrappers.hpp

@@ -23,6 +23,7 @@
 #include <QThread>
 #include <obs.hpp>
 
+#include <functional>
 #include <memory>
 #include <vector>
 
@@ -64,6 +65,8 @@ QDataStream &operator>>(QDataStream &in, OBSScene &scene);
 QDataStream &operator<<(QDataStream &out, const OBSSceneItem &si);
 QDataStream &operator>>(QDataStream &in, OBSSceneItem &si);
 
+QThread *CreateQThread(std::function<void()> func);
+
 class SignalBlocker {
 	QWidget *widget;
 	bool blocked;