Add new notebook command to command palette
Add new notebook command to command palette

There is a `Console` command that starts a new console, so it seems
to make sense to have a corresponding `Notebook` command that starts
a new notebook.

Issues was raised by @MMesch on gittter

https://gitter.im/jupyterlab/jupyterlab?at=5b363d4abe98b1422413c3a3

jupyter/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab