Restructure the entire editor codebase to consistently match the message hierarchy

Closes #744

editor/src/messages/broadcast/broadcast_event.rs

@@ -0,0 +1,11 @@
+use crate::messages::prelude::*;
+
+use serde::{Deserialize, Serialize};
+
+#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize, Hash)]
+#[impl_message(Message, BroadcastMessage, TriggerEvent)]
+pub enum BroadcastEvent {
+	DocumentIsDirty,
+	ToolAbort,
+	SelectionChanged,
+}