feat: Add possibility to downgrade from biometrics to password pin security

[pierobassa]

Currently once biometrics is set, it is not possible to use password pin as a security method. This was thought to be desired due to it downgrading the security level.

Though, the user should be able to choose whether to downgrade or not.

A real world example would be having Touch ID (Fingerprint on Android) and having fingerprints of different people saved. Thus access to the wallet is possible even by someone else (e.g., a daughter that has access to play games).

So having password pin as a security method solves undesired access from others that are saved with device's biometrics.

Also on a UI perspective, the toggle to Password pin wouldn't be disabled and the user wouldn't ask himself why it's disabled.

[fabiofvc]

To be discussed.
@davidecarpini is positive
@grenos have some doubt.