Initialize BufferManager from within Mixer

Avoid crashes caused by worker threads accessing the buffer manager
before it is initialized. Therefore initialize it from within the
Mixer constructor which has the side effect that it gets initialized
in console-only rendering mode as well.

include/BufferManager.h

@@ -40,7 +40,7 @@ const int BM_INITIAL_BUFFERS = 512;
 class EXPORT BufferManager
 {
 public:
-	static void init();
+	static void init( fpp_t framesPerPeriod );
 	static sampleFrame * acquire();
 	static void release( sampleFrame * buf );
 	static void refresh();