renderer: switched audio rendering over to planar buffers

While planar audio cannot be used for playback, it's much easier for processing.
This should lead to cleaner and easier to write code in the future.

app/node/node.h

@@ -26,6 +26,7 @@
 #include <QPointF>
 #include <QXmlStreamWriter>
 
+#include "codec/samplebuffer.h"
 #include "common/rational.h"
 #include "common/xmlutils.h"
 #include "node/dependency.h"
@@ -190,7 +191,7 @@ public:
   /**
    * @brief If ProcessesSamples() is true, this is the function that will process them.
    */
-  virtual void ProcessSamples(const NodeValueDatabase *values, const AudioRenderingParams& params, const float* input, float* output, int index) const;
+  virtual void ProcessSamples(const NodeValueDatabase *values, const AudioRenderingParams& params, const SampleBufferPtr input, SampleBufferPtr output, int index) const;
 
   /**
    * @brief Returns the parameter with the specified ID (or nullptr if it doesn't exist)