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/Weather/WeatherMgr.cpp

@@ -21,12 +21,13 @@
 */
 
 #include "WeatherMgr.h"
-#include "Weather.h"
+#include "DatabaseEnv.h"
 #include "Log.h"
+#include "MiscPackets.h"
 #include "ObjectMgr.h"
 #include "Player.h"
+#include "Weather.h"
 #include "WorldSession.h"
-#include "MiscPackets.h"
 
 namespace WeatherMgr
 {