Hide username field by default, add conf setting to control visibilty

[wltjr]

The username field should be hidden by default, only allowing found users to be selected via avatar and password entered. Though not a fan of the avatars, they may stay or go. A setting should be added to control if the username field should be shown or not. Needed to log in non users like root. Presently root or anyone can log in via typing in a name. That should be changed. Maybe even an option to click to make a password visible and no configuration option. More like a show this password, show username field button. Either way username should not be visible by default. It may have been this way originally before my modifications.