For sensors with internal storage we may want to garbage collect prints.
Adding this API means we can list all local prints, allowing us to find
out whether there are prints on the device's storage with no
corresponding print on the host.
- Remove SetUsername itself, and add a username parameter to DeviceClaim,
ListEnrolledFingers and DeleteEnrolledFingers.
- For each of those calls, check that the incoming connection is allowed
to operate on that particular username
- Don't require a claimed device to list or remove fingerprints
- Clean up username and sender when releasing the device
- Modify the storage backend to not require an opened device to list
or delete fingerprints
- Add a simple test program to list registered fingerprints for the
usernames passed as argument
