Refactor SECLAL player into new threaded player class

The reason for moving the implementation out from CSoundGenerator into
its own class is, because CSoundGenerator was a very complex and
obscure class. It mixed many tasks in one place. CSelcalPlayer
is designed to play SELCALs only.

The following design changes have been made, compared to CSoundGenerator:
* Use pull mode instead of push mode. QBuffer is used as the QIODevice and
  is a wrapper around QByteArray. Therefore it is not necessary to
  implement our own QIODevice.
* Internally it uses a CThreadedSelcalPlayer to relieve the load of the
  main thread. CThreadedSelcalPlayer inherits CContinuousWorker, no
  low level QThread implementation was necessary.
* Push mode was not implemented.
* It is important that the QAudioOutput is allocated in the worker thread.
  QAudioOutput allocates internal objects, which cannot be moved to
  the worker thread.
* Data caching. The generated seclal audio data is cached.

refs #736

src/blacksound/tonepair.h

@@ -0,0 +1,55 @@
+/* Copyright (C) 2016
+ * swift project Community / Contributors
+ *
+ * This file is part of swift project. It is subject to the license terms in the LICENSE file found in the top-level
+ * directory of this distribution and at http://www.swift-project.org/license.html. No part of swift project,
+ * including this file, may be copied, modified, propagated, or distributed except according to the terms
+ * contained in the LICENSE file.
+ */
+
+//! \file
+
+#ifndef BLACKSOUND_TONEPAIR_H
+#define BLACKSOUND_TONEPAIR_H
+
+#include "blacksoundexport.h"
+#include "blackmisc/pq/frequency.h"
+#include "blackmisc/pq/time.h"
+
+#include <tuple>
+
+namespace BlackSound
+{
+    //! Tone pair to be played
+    class BLACKSOUND_EXPORT CTonePair
+    {
+    public:
+        //! Play two tones with frequencies f for t milliseconds
+        CTonePair(const BlackMisc::PhysicalQuantities::CFrequency &frequency,
+              const BlackMisc::PhysicalQuantities::CFrequency &secondaryFrequency,
+              const BlackMisc::PhysicalQuantities::CTime &duration);
+
+        //! Get frequency of the first tone
+        int getFirstFrequencyHz() const { return m_firstFrequencyHz; }
+
+        //! Get frequency of the second tone
+        int getSecondFrequencyHz() const { return m_secondFrequencyHz; }
+
+        //! Get play duration
+        qint64 getDurationMs() const { return m_durationMs; }
+
+        //! Comparison operator
+        friend bool operator <(const CTonePair& lhs, const CTonePair& rhs)
+        {
+            return std::tie(lhs.m_firstFrequencyHz, lhs.m_secondFrequencyHz, lhs.m_durationMs)
+                    < std::tie(rhs.m_firstFrequencyHz, rhs.m_secondFrequencyHz, rhs.m_durationMs);
+        }
+
+    private:
+        int m_firstFrequencyHz;  //!< first tone's frequency, use 0 for silence
+        int m_secondFrequencyHz; //!< second tone's frequency, or 0
+        qint64 m_durationMs;     //!< How long to play (duration)
+    };
+}
+
+#endif // guard