Prefer biometric authentication when possible over Passwords

[wdawgnc]

Quite a number of Android devices support biometric authentication, typically with a fingerprint reader. Incognoto should prefer that form of authentication over passwords due to its increased security posture. Passwords should be the least safe fallback if the device or the user (weird if they're using Incog one would presume they care about security) cant/doesn't want to use biometrics.