Bump up AggregationPerZoomStep to 10 again

Thought using 2 would help performance (when rendering). Maybe it does, but it's still quite slow when rendering a bunch of thumbnails at once.

include/SampleThumbnail.h

@@ -79,7 +79,7 @@ class LMMS_EXPORT SampleThumbnail
 	class Thumbnail
 	{
 	public:
-		static constexpr auto AggregationPerZoomStep = 2;
+		static constexpr auto AggregationPerZoomStep = 10;
 
 		struct Peak
 		{