Upgrade cell's `editable` and `deletable` metadata if not defined

notebook/static/notebook/js/cell.js

@@ -494,6 +494,14 @@ define([
         if (data.metadata !== undefined) {
             this.metadata = data.metadata;
         }
+        // upgrade cell's editable metadata if not defined
+        if (this.metadata.editable === undefined) {
+          this.metadata.editable = this.is_editable();
+        }
+        // upgrade cell's deletable metadata if not defined
+        if (this.metadata.deletable === undefined) {
+          this.metadata.deletable = this.is_deletable();
+        }
     };