Remove placeholder objects for subfolders

A subfolder in a container is now represented solely by the prefix of
an object name delimited by a forward-slash (/). If an object exists
in a container that matches the implied subfolder of another object,
each will be displayed in the objects table.

Implements bp swift-folder-prefix

Change-Id: I05252c1db34fdf6584a71e8827ff6f8363bf0488
Merge "Remove placeholder objects for subfolders"