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/render/videoparams.cpp

@@ -34,6 +34,12 @@ VideoRenderingParams::VideoRenderingParams() :
 {
 }
 
+VideoRenderingParams::VideoRenderingParams(const int &width, const int &height, const PixelFormat::Format &format) :
+  VideoParams(width, height, rational()),
+  format_(format)
+{
+}
+
 VideoRenderingParams::VideoRenderingParams(const int &width, const int &height, const rational &time_base, const PixelFormat::Format &format, const RenderMode::Mode& mode, const int &divider) :
   VideoParams(width, height, time_base),
   format_(format),