Add verification using decrypted nfskey

[drizzt]

It's quite a PoC, but I think it's a nice feature to have

[llakssz]

Thanks for the work but I'm not sure if I will merge this - if I was using decrypted title keys sure... it is good to verify them.
But we are only using encrypted title keys, so whether the decryption title key is valid or not... that is a different problem. It's not useful because the only way of seeing if a dec and enc key are the same key is using a 3ds.
Using a good tool that only dumps valid shop bought enc keys, like the latest Decrypt9, or a trusted source that dumps the dec keys, checks them and then re-encrypts them, the encrypted title keys will be correct.