tweak export to notebook; add flags stubs code to allow them to work in a notebook

ortools/python/ortools_notebook.py

@@ -16,9 +16,9 @@
 import re
 import sys
 
-from notebook import notebookapp
+from notebook import app
 
 
 if __name__ == "__main__":
     sys.argv[0] = re.sub(r"(-script\.pyw?|\.exe)?$", "", sys.argv[0])
-    sys.exit(notebookapp.main())
+    sys.exit(app.main())