Add support for undeleteable cells
Add support for undeleteable cells

jupyter/jupyterlab,jupyter/jupyterlab,eskirk/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab,eskirk/jupyterlab,charnpreetsingh185/jupyterlab,charnpreetsingh185/jupyterlab,charnpreetsingh185/jupyterlab,eskirk/jupyterlab,charnpreetsingh185/jupyterlab,charnpreetsingh185/jupyterlab,eskirk/jupyterlab,jupyter/jupyterlab,eskirk/jupyterlab