Password field changes to required on ajax load

The plugin configuration gets reset and therefore the password will be empty and the field will be required. This creates an error when saving the form, because the password field is not filled out.

Even though the saferpay payment gateway form doesn't use ajax by default, other modules could extend the form and adding ajax to this would brake the form.

As discussed with @berdir, makes sense to remove the special password hiding feature and just show the password like other gateways do.