[16.0][REV] password_security: Restore password_estimate.

[amh-mw]

This reverts commit c8d5d68 which should not have removed password_estimate as part of the migration to 16.0. #482

I do think it is worth having the conversation raised by @astirpe in #482 (comment)

I just found out that when a new user is trying to signup by entering a very large password, there is a critical performance issue.
It's caused by the adoption of zxcvbn library, in particular the execution of this line https://github.com/dwolfhub/zxcvbn-python/blob/master/zxcvbn/__init__.py#L25 is very slow. That could potentially cause a DDOS attack in my opinion.
Probably that's also the reason of #487 but I didn't investigate in deep that issue.
So I'm going to remove the password estimate check functionality from this module and also remove the dependency on zxcvbn, because the password estimation is already provided by "Password Meter" widget by standard Odoo.