Massively reorganize and clean up the whole Rust codebase (#478)

* Massively reorganize and clean up the whole Rust codebase

* Additional changes during code review

editor/src/document/artboard_message.rs

@@ -0,0 +1,20 @@
+use crate::message_prelude::*;
+
+use graphene::Operation as DocumentOperation;
+
+use serde::{Deserialize, Serialize};
+
+#[remain::sorted]
+#[impl_message(Message, DocumentMessage, Artboard)]
+#[derive(PartialEq, Clone, Debug, Serialize, Deserialize)]
+pub enum ArtboardMessage {
+	AddArtboard { top: f64, left: f64, height: f64, width: f64 },
+	DispatchOperation(Box<DocumentOperation>),
+	RenderArtboards,
+}
+
+impl From<DocumentOperation> for ArtboardMessage {
+	fn from(operation: DocumentOperation) -> Self {
+		Self::DispatchOperation(Box::new(operation))
+	}
+}