Use C++11 enum class

src/core/thread.h

@@ -31,7 +31,7 @@ class Thread : public QThread {
   Q_OBJECT
 
  public:
-  explicit Thread(QObject *parent = nullptr) : QThread(parent), io_priority_(Utilities::IOPRIO_CLASS_NONE) {}
+  explicit Thread(QObject *parent = nullptr) : QThread(parent), io_priority_(Utilities::IoPriority::IOPRIO_CLASS_NONE) {}
 
   void SetIoPriority(Utilities::IoPriority priority) {
     io_priority_ = priority;