List of notebook files should include more file information

From the File tab of the root view we see a list of files in the current directory.

It would be useful to see more information about files, e.g. have a button to toggle between the existing "ls -1" style and "ls -altr" style outputs.

In the case of notebooks in that list, it would also be nice to know the number of cells in notebooks (and why not the kernel).

The use case for this is that when experimenting we can end up with a lot of Untitled files that can probably be deleted ... it would be nice to have some indication of contents without having to open each file.