Display Configuration Settings UI

Display Configuration need an UI to override values.

Now my yml file show this.

`display_configuration:
  widget_ids:
    735d146c-a4b2-4327-a057-d109e0905e05: 'Upload files'
    a4ad947c-9669-497c-9988-24351955a02f: 'Files listing'
  width: 80
  height: 550
  link_text: 'Select files'
  auto_open: true`

What I like is the width to be `width: '80%'` I'm using the modal widget.
