Add mixins for blocks that rotate based on player yaw at placement

Also add observer block handler.

src/Blocks/BlockObserver.h

@@ -0,0 +1,19 @@
+
+#pragma once
+
+#include "BlockHandler.h"
+#include "Mixins.h"
+
+
+class cBlockObserverHandler:
+	public cClearMetaOnDrop<cPitchYawRotator<cBlockHandler>>
+{
+	using super = cClearMetaOnDrop<cPitchYawRotator<cBlockHandler>>;
+
+public:
+
+	cBlockObserverHandler(BLOCKTYPE a_BlockType) : super(a_BlockType)
+	{
+	}
+
+};