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/SafariZone_Southwest/scripts.inc

@@ -2,10 +2,10 @@ SafariZone_Southwest_MapScripts:: @ 823D266
 	.byte 0
 
 SafariZone_Southwest_EventScript_23D267:: @ 823D267
-	msgbox SafariZone_Southwest_Text_2A53B7, 2
+	msgbox SafariZone_Southwest_Text_2A53B7, MSGBOX_NPC
 	end
 
 SafariZone_Southwest_EventScript_23D270:: @ 823D270
-	msgbox SafariZone_Southwest_Text_2A5613, 3
+	msgbox SafariZone_Southwest_Text_2A5613, MSGBOX_SIGN
 	end