* Allow FPI_PRINT_NBIS to be extended rather than overridden if a user
supplies an existing FpPrint template with data;
* Prints will only be extended if a device has the required feature.
For image-based devices this feature is added by default since they
typically do not have storage (this can be overridden at the child
class level).
Extending an existing FpPrint requires passing a template print with
existing data during the enrollment process. This is done because the
caller is responsible for maintaining the fingerprint database and doing
the necessary deserialization operations if needed. The existing
example program is updated to show how to do that.
