Use Bcrypt instead of MD5/plaintext

[vstumpf]

Related to rathena/rathena#7650

We save and check bcrypt instead of MD5.
This is a breaking change, as we're forcing the use of bcrypt.

[sanasol]

I think we should keep old schema for legacy users.
But make it optional and set bcrypt as new default.

And I see there is additional check for passwd_type = 2 (bcrypt + md5) that must handled also.