Change the path to create notebooks in when navigating directories

[takluyver]

Closes gh-3263
Closes gh-3248

There's still an issue where the dashboard goes back to showing the root directory when you create a notebook. I'll look into that later.

[takluyver]

I haven't fully understood the issue with the list showing the previous directory yet, but what I have found is that:

• I can trigger it by creating a new text file or a directory, as well as a new notebook.
• The onpopstate() handler we add is getting called, for some reason.

[takluyver]

Educated guesswork led me to use event.preventDefault() on the links that make new files and folders, which seems to fix the issue with the files list jumping back to a previous state.

[takluyver]

@gnestor @Carreau if you have a chance to review this, I think the issue is worth doing a 5.3.2 bugfix release for. I can make the release tomorrow if this gets merged.

[Carreau]

Haven't looked at notebook codebase in a while but this look good to me.
Happy if we make a 5.3.2.

[gnestor]

Thanks for fixing this @takluyver! I think that releasing a patch for this is a good idea as it's a regression that was reported by several people. Let me know if I can help with that 👍

[takluyver]

I've released 5.4 to PyPI with the fix (and a few other changes). Now to update conda-forge.