[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/set/flymode.cpp

@@ -51,7 +51,7 @@ void SetFlymode(Client *c, const Seperator *sep)
 	}
 
 	t->SetFlyMode(static_cast<GravityBehavior>(flymode_id));
-	t->SendAppearancePacket(AT_Levitate, flymode_id);
+	t->SendAppearancePacket(AppearanceType::FlyMode, flymode_id);
 
 	const uint32 account = c->AccountID();