Further - almost there.

Working:
- Able to create folders, at top level and inside created folders
- Able to enter folders, recursively
- Able to add contents to folders, including subfolders
- Able to edit and delete folder contents, etc
- Able to go back out of entered folders, reenter them, preserving contents

Not yet working:
- ** Created folders break across logins - become "undefined" entries
  with "undefined" type
- Created folders automatically get a spurious entry, "undefined", with
  undefined type.
- No UI to rename, delete folders
- Folder back should be a distinct back button, rather than a menu item