Ability to lock a site or a note

[TwiNNatioN]

While I do know that it's possible to recover a deleted, non-purged site/secure note, I'd still like to have the option to lock an entry.

A locked entry:
- Cannot be deleted
- Cannot be modified

Unlocking an entry would require re-authentication using the master password as well as a multi-factor authentication method, if available, regardless of whether the current device is "trusted for 30 days" or not.