New feature: Add fingerprint scanner support

[Fleuv]

Describe the issue

The last few years fingerprint scanners and other identity validation technologies have been moved into smartphones. Thus soon or later the request for a fingerprint scanner or facial recognition sign-in method to the IRMA app will be raised. Currently the app supports signing in via an app specific PIN code. Will it be possible to replace this for a fingerprint scanner check?

Test case

Steps to reproduce

Scenario A: When the user doesn't have an IRMA account yet:

1. Open the app and create a new account.
2. Enter your pin code and complete next steps.
3. Sign in to the app with your PIN code.

Scenario B: When the user does have an IRMA account:

1. Open the IRMA app and sign in with your PIN code.
2. Open the menu and select "Change pin".
3. Enter your current and new PIN.

Expected result

At step A2 and B2 there should be an option to toggle change the authentication method to fingerprint scanner.

Actual result

There is only an option to use a PIN code as authentication method.