Changes to GStreamer backend for audio decoder.

Removed WaitingState.
New signals: finished(), positionChanged(), durationChanged().
New methods: position(), duration().
A parameter removed from read() method.
Unit tests updated.

Change-Id: Ie9d8a2804285c5542e592cce69963adbdf6ebfb8
Reviewed-by: Jonas Rabbe <jonas.rabbe@nokia.com>
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>

src/plugins/gstreamer/audiodecoder/qgstreameraudiodecodercontrol.h

@@ -80,9 +80,12 @@ public:
     QAudioFormat audioFormat() const;
     void setAudioFormat(const QAudioFormat &format);
 
-    QAudioBuffer read(bool *ok);
+    QAudioBuffer read();
     bool bufferAvailable() const;
 
+    qint64 position() const;
+    qint64 duration() const;
+
 private:
     // Stuff goes here