add jupyter extensions to userprofile handler

Author: oliver-sanders

cylc/uiserver/handlers.py

@@ -281,6 +281,13 @@ def get(self):
             user_info['mode'] = 'single user'
         else:
             user_info['mode'] = 'multi user'
+
+        user_info['extensions'] = {
+            y.name: y.default_url
+            for x in self.serverapp.extension_manager.extension_apps.values()
+            for y in x if getattr(y, 'default_url', '/') != '/'
+        }
+
         self.write(json.dumps(user_info))