It seems pointless to have two identity-related concepts in parallel.
The new approach is as follows: The identifier is a Core::Id. If the
client code supplies a fingerprint string (as needed for auto-detected
devices), the id is derived from it, otherwise it gets created from a
newly generated UUID.

Change-Id: I680afa6cd2fdd43ec1c461616ba982b3ff55c73a
Reviewed-by: Tobias Hunger <tobias.hunger@nokia.com>