General: Normalize several headers' include paths

Normalizes the include paths and makes them consistent. Also adds any
missing includes relevant to the interface.

Runtime/Particle/CIntElement.hpp

@@ -1,6 +1,9 @@
 #pragma once
 
-#include "IElement.hpp"
+#include <memory>
+#include <vector>
+
+#include "Runtime/Particle/IElement.hpp"
 
 /* Documentation at: http://www.metroid2002.com/retromodding/wiki/Particle_Script#Int_Elements */