Add back missing singletons

app/package.json

@@ -39,7 +39,6 @@
     "@jupyterlab/docmanager": "~3.0.7",
     "@jupyterlab/docmanager-extension": "~3.0.7",
     "@jupyterlab/documentsearch": "~3.0.8",
-    "@jupyterlab/documentsearch-extension": "~3.0.8",
     "@jupyterlab/filebrowser": "~3.0.7",
     "@jupyterlab/fileeditor": "~3.0.7",
     "@jupyterlab/fileeditor-extension": "~3.0.7",
@@ -48,6 +47,8 @@
     "@jupyterlab/mathjax2-extension": "~3.0.7",
     "@jupyterlab/notebook": "~3.0.7",
     "@jupyterlab/notebook-extension": "~3.0.7",
+    "@jupyterlab/observables": "~4.0.3",
+    "@jupyterlab/outputarea": "~3.0.6",
     "@jupyterlab/rendermime": "~3.0.6",
     "@jupyterlab/rendermime-extension": "~3.0.7",
     "@jupyterlab/rendermime-interfaces": "~3.0.5",
@@ -172,6 +173,8 @@
       "@jupyterlab/fileeditor",
       "@jupyterlab/mainmenu",
       "@jupyterlab/notebook",
+      "@jupyterlab/observables",
+      "@jupyterlab/outputarea",
       "@jupyterlab/rendermime",
       "@jupyterlab/rendermime-interfaces",
       "@jupyterlab/services",