Rearrange layers refactor (#281)

* Keep selection during reordering

* Fix paste layer selection

* Remove junk from layer matadata

* Add function to get non_selected_layers

* Cleanup

* Add tests

core/document/src/operation.rs

@@ -51,6 +51,7 @@ pub enum Operation {
 	PasteLayer {
 		layer: Layer,
 		path: Vec<LayerId>,
+		insert_index: isize,
 	},
 	AddFolder {
 		path: Vec<LayerId>,
@@ -80,8 +81,4 @@ pub enum Operation {
 		path: Vec<LayerId>,
 		color: Color,
 	},
-	ReorderLayers {
-		source_paths: Vec<Vec<LayerId>>,
-		target_path: Vec<LayerId>,
-	},
 }