Vulnerability: Add a SampleLoader that prevents negative attack scores computation

Adds a references list to the samples to prevent attack probes to be compared to every reference.

Ping @lcolbois, and sorry for the confusion.

Thanks @ydayer ! That was quick

@ydayer why the replaymobile implementation is not using this: https://gitlab.idiap.ch/bob/bob.bio.face/-/blob/e9fbd67a4faee4d58dd3d5a931397f5141ef0b93/bob/bio/face/database/replaymobile.py

ok I see the same code in there too.

merged

mentioned in commit 103385a3

mentioned in issue bob#269 (closed)