Event broadcasting system (#692)

* broadcast system implemented but not everywhere

* unused types

* code review with keavon

* - optional signal mappings
- tool.rs simplification

* Cleanup

* reduced code duplication in `tool.rs`

* ran cargo fmt

* code review changes

* fix merge error

Co-authored-by: Keavon Chambers <keavon@keavon.com>

editor/src/communication/broadcast_message.rs

@@ -0,0 +1,26 @@
+use crate::message_prelude::*;
+
+use serde::{Deserialize, Serialize};
+
+#[impl_message(Message, Broadcast)]
+#[derive(PartialEq, Clone, Debug, Serialize, Deserialize)]
+pub enum BroadcastMessage {
+	SubscribeSignal {
+		on: BroadcastSignal,
+		send: Box<Message>,
+	},
+	UnsubscribeSignal {
+		on: BroadcastSignal,
+		message: Box<Message>,
+	},
+	#[child]
+	TriggerSignal(BroadcastSignal),
+}
+
+#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize, Hash)]
+#[impl_message(Message, BroadcastMessage, TriggerSignal)]
+pub enum BroadcastSignal {
+	DocumentIsDirty,
+	ToolAbort,
+	SelectionChanged,
+}