adds constants, cleans up callstd and msgbox code

* adds some constants for standard script names and messagebox types
* replaces some callstd calls with msgbox calls where equivalent
* replaces msgbox and callstd calls using raw digits with versions that use the constants

data/maps/InsideOfTruck/scripts.inc

@@ -50,7 +50,7 @@ InsideOfTruck_EventScript_23BF46:: @ 823BF46
 	end
 
 InsideOfTruck_EventScript_23BF6C:: @ 823BF6C
-	msgbox InsideOfTruck_Text_23BF75, 3
+	msgbox InsideOfTruck_Text_23BF75, MSGBOX_SIGN
 	end
 
 InsideOfTruck_Text_23BF75: @ 823BF75