[Commands] Cleanup #appearance Command (#3827)

* [Commands] Cleanup #appearance Command

# Notes
- Cleanup messages and logic.
- Cleanup appearance type constants to use a namespace with constexpr instead.
- Cleanup animation constants to use a namespace with constexpr instead.

* Update emu_constants.cpp

* Cleanup

zone/gm_commands/acceptrules.cpp

@@ -8,6 +8,6 @@ void command_acceptrules(Client *c, const Seperator *sep)
 	}
 
 	database.SetAgreementFlag(c->AccountID());
-	c->SendAppearancePacket(AT_Anim, ANIM_STAND);
+	c->SendAppearancePacket(AppearanceType::Animation, Animation::Standing);
 	c->Message(Chat::White, "It is recorded you have agreed to the rules.");
 }