waveformview: made UI seekable

app/render/backend/audiorenderbackend.cpp

@@ -27,6 +27,8 @@ void AudioRenderBackend::SetParameters(const AudioRenderingParams &params)
 
   // Regenerate the cache ID
   RegenerateCacheID();
+
+  emit ParamsChanged();
 }
 
 void AudioRenderBackend::ConnectViewer(ViewerOutput *node)

app/render/backend/audiorenderbackend.h

@@ -24,6 +24,9 @@ public:
 
   QString CachePathName();
 
+signals:
+  void ParamsChanged();
+
 protected:
   virtual void ConnectViewer(ViewerOutput* node) override;