Core/Game: Include cleanup

* Mostly aimed at removing Log/DatabaseEnv includes from other headers
* Fix most packet headers including other packet headers - moved common structures such as ItemInstance to their own files
* Moved SAI function definitions to source files (massive or requiring many different dependencies)

src/server/game/Chat/ChatLink.cpp

@@ -16,6 +16,7 @@
  */
 
 #include "ChatLink.h"
+#include "Log.h"
 #include "SpellMgr.h"
 #include "ObjectMgr.h"
 #include "SpellInfo.h"