Request personal-files interface for yubioath-desktop

Yubico Authenticator uses the .ykman folder in $HOME to store saved password hashes for a specific YubiKey, if the user requests this. It shares this folder with the command line tool ykman (yubikey-manager), that has the same functionality, and is used as a library by Yubico Authenticator.

Relevant code:

Snapcraft file:

Withdrawing this request, I can use SNAP_USER_DATA for this purpose instead.