#12 restructure favorite locations to shared locations

[Scott Cameron]

* make Favorites directory a special virtual directory
(dotfile)

* store favorites, group spaces, dropboxes, and shared

* Get rid of the concept of having an actual
"favorites" folder stored in
the user's AFS space. Create new, easily identified
virtual folders that
may have additional, context-sensitive options that
would be displayed in the left-hand bar. These folders
will eventually include favorites, groups, shared and
dropboxes

* Add an "add this folder as a favorite" link as a
context-sensitive action.

* store list of places that someone else has permitted
to a user in a database (both for umich users as well
as friends)