Ring::Role::Number returns bestId instead of URI

Whenever possible, we should be displaying the registered name
instead of the RingID. We make the Ring::Role::Number data role
use getBestId() instead of uri(). The user can still explicitly
ask for the Uri if needed.

Change-Id: I9dda876bff9c6dbe293f40781c5c388b7ec1bb2a
Reviewed-by: Nicolas Jäger <nicolas.jager@savoirfairelinux.com>