Adds custom emotes to slimes (#320)

Does not add the other human emotes, since they seem a bit odd to put
in.
Slimes needs custom emotes for... reasons. You all know why, don't make
me say it in writing! >_<

code/modules/mob/living/emote.dm

@@ -376,6 +376,7 @@
 	key = "me"
 	key_third_person = "custom"
 	message = null
+	mob_type_blacklist_typecache = list(/mob/living/brain)
 
 /datum/emote/living/custom/proc/check_invalid(mob/user, input)
 	. = TRUE