Disabled input fields are not distinguished in any way

Disabled input fields should have the same design as read-only fields, only with a slightly lighter text. Otherwise, it's unclear why all of a sudden an input is not editable. A couple of such places are: 1. disabled confirmation message input in the script configuration form, 2. disabled post and variable fields in web scenario step configuration form if the "Retrieve only headers" checkbox is checked. We should also check for other similar places.