Require additional authentication before unlocking saved DiceKey

[UppaJung]

When a user saves a DiceKey on the Electron desktop app, it should be stored in the credential store with a flag that requires the use of additional authentication before unlocking.

Requires adding support for this into the keytar package.
atom/node-keytar#405

On MacOS, see:
https://developer.apple.com/documentation/localauthentication/accessing_keychain_items_with_face_id_or_touch_id

For Windows:
???
keytar should not use set Credential.Persist=CRED_PERSIST_ENTERPRISE, but instead CRED_PERSIST_LOCAL_MACHINE so that DiceKeys aren't moved between machines.