Restructure the entire editor codebase to consistently match the message hierarchy

Closes #744

editor/src/messages/broadcast/broadcast_message.rs

@@ -0,0 +1,23 @@
+use crate::messages::prelude::*;
+
+use serde::{Deserialize, Serialize};
+
+#[remain::sorted]
+#[impl_message(Message, Broadcast)]
+#[derive(PartialEq, Clone, Debug, Serialize, Deserialize)]
+pub enum BroadcastMessage {
+	// Sub-messages
+	#[remain::unsorted]
+	#[child]
+	TriggerEvent(BroadcastEvent),
+
+	// Messages
+	SubscribeEvent {
+		on: BroadcastEvent,
+		send: Box<Message>,
+	},
+	UnsubscribeEvent {
+		on: BroadcastEvent,
+		message: Box<Message>,
+	},
+}