text: Title: Removed notebooks remain in the Mercury
  Body: I'm running Mercury locally. I had `eda.ipynb` file in the directory. It was served fine in the Mercury. I renamed the notebook file. Now, in the Mercury I had two notebooks, with old and new name. The notebook with old name was not working in the Mercury. The new one is working fine.
  
  There should be some check if notebook is still available when starting Mercury locally.