Login.prototype.setErrors = function setErrors(opts) {
    var control_username = $('#control-username')
    var control_password = $('#control-password')
    if (opts.username_error) control_username.addClass('error')
    else                     control_username.removeClass('error')
    if (opts.password_error) control_password.addClass('error')
    else                     control_password.removeClass('error') }