Elias Holzmann

This adds just tests (and changes some visibilities where necessary) – I found no requests that weren't already meeting the canonicalization requirements, so the behavior of the lib itself stays...

Use `ykman` instead of `yubikey-personalization`

12

Currently, this project uses the YubiKey Personalization Tool which is [no longer under active development](https://www.yubico.com/support/download/yubikey-personalization-tools/). It would be nice for `yubikey-full-disk-encryption` to instead use [YubiKey Manager](https://www.yubico.com/support/download/yubikey-manager/) which has more features....

Fixed typo

1

The AppState::clear_completed method was incorrectly called AppState::clear_completed_button. (clear_completed_button is the button, not the method)