Updated hashing

[ghost]

Satisfies #262

[gwarf]

I've tested this with a MariaDB database, and it fails saying that Argon2 hash is too long for the length of the pwhash column that is at 48.
Didn't checked much to find what's the appropriate length, but it works with a length of 120.

[gwarf]

Apparently this is also breaking other things, like the challenge creation, due to another issue with the column size, and the validation in validate_answer in the static_argon2.py, argon2.PasswordHasher().hash getting more parameters than expected.