Display name of resource as virtual filesystem root

[timkpaine]

Right now we hash our resources and represent that as a drive. We should switch to using the name of the resource as the root

So e.g. right now if i add a resource to the file browser, it will show as /. We should make it so that if a resource named "blerg" is added to the sidebar, it shows as a folder /blerg, and disallows creation of files/folders at that top level /.

Needs: #248
xref: #195

Should also solve #210 which doesn't seem to be a bug in jupyter-fs but just the default jupyter behavior when you download stuff from the root level. No root level things, no accidental inclusion of the drive (hash).