The actual renaming is easier to do in BooksShelf rather than BooksPathModel
and it generally makes more sense.
Editing now also starts after long-pressing the title of the current folder.
UI doesn't allow creating or renaming the folders yet and there's
no easy way to move books between folders, but if folders are there,
they will be shown and the user will be able to navigate between them.
Folders can be deleted though.
