Implement a much better way to distinguish the account ("my") share rooms'
list and base urls:

 - assign the list url to the collection's ".url" attribute
 - assign the content item's base url to a (new) collection's ".urlBase"
   attribute
 - make the file Folders views prefer a collection's .urlBase over its .url
   attribute.

This works, without changing the collection's url mid-stream.

(It would be good to shift the devices/storage stuff over to use .urlBase,
as well.)