#951 Add an option to show a password prompt right away for a single user

[Artem S. Tashkinov]

Please implement this is an option or make it default - whatever fits you.

So, whenever LXDM discovers that there's just a single user in the system, then show the password prompt right away, instead of asking the user to select the only user on the system which is an extra redundant click.

Thank you!