Move the Worker password hashing/comparison functions into a struct, and
use it via an interface. This will make it easier to switch to different
hashing algorithms.
Even with a low number of iterations, BCrypt is quite slow. That's good for
security, but not for Flamenco Worker authentication -- the password is
more as "nice check to avoid accidentally reusing the same ID" than
something for security.
The add-on code was copy-pasted from other addons and used the GPL v2
license, whereas by accident the LICENSE text file had the GNU "Affero" GPL
license v3 (instead of regular GPL v3).
This is now all streamlined, and all code is licensed as "GPL v3 or later".
Furthermore, the code comments just show a SPDX License Identifier
instead of an entire license block.
