[Feature Request] Add auto-locking of wallet

[RequestPrivacy]

Description

In addition to the currently supported manual locking of the wallet(s) an auto-lock feature would be nice. A slider for setting the time interval after which all wallets will be locked could be realized in the View Menu (where the locking can manually be activated right know) although the place isn't intuitive for such a setting. Maybe better to apply it to the Preferences section?!