Reduce history system's excessive memory usage from storing copies of images each step (#845)

* Limit saved undo history

* Do not commit path every mouse move event

* Reference count images in history system instead of cloning the image data

* Increase history storage step limit to 100

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

editor/src/messages/frontend/utility_types.rs

@@ -15,8 +15,8 @@ pub struct FrontendDocumentDetails {
 pub struct FrontendImageData {
 	pub path: Vec<LayerId>,
 	pub mime: String,
-	#[serde(rename = "imageData")]
-	pub image_data: Vec<u8>,
+	#[serde(skip)]
+	pub image_data: std::rc::Rc<Vec<u8>>,
 }
 
 #[derive(Clone, Copy, Debug, Default, Eq, PartialEq, Serialize, Deserialize)]