Customize interface: better face editor

[Per Abrahamsen]

The current face editor looks like this (in the -nw version, which
currently work better than the windowing version):

    Widget Button Face:(sample) [Hide]
       [State]: you have edited the value as text, but you have not set the fac
    Face used for widget buttons.
    Parent groups: [Widget Faces]
    Attributes: [ ] Font family: [Value Menu] *
                [ ] Width: [Value Menu] *
                [ ] Height: [Value Menu] *
                [X] Weight: [Value Menu] bold
                [ ] Slant: [Value Menu] *
                [ ] Underline: [Value Menu] *
                [ ] Overline: [Value Menu] *
                [ ] Strike-through: [Value Menu] *
                [ ] Box around text: [Value Menu] *
                [ ] Inverse-video: [Value Menu] *
                [ ] Foreground: [Value Menu] *
                [ ] Background: [Value Menu] *
                [ ] Stipple: [Value Menu] *
                [ ] Inherit:
                    [INS]

I wonder if it would look better as:

    Widget Button Face: (sample) [Hide]
       [State]: you have edited the value as text, but you have not set the fac
    Face used for widget buttons.
    Parent groups: [Widget Faces]
    Inherit attributes from these faces:
    [INS]
    Attributes of this face:
    [DEL] Weight: [Value Menu] bold
    [Add attribute]

Pressing "Add attribute" would pop-up a list of attributes.  If you
selected e.g. "Foreground" from that list, the display would change
to: 

    Widget Button Face: (sample) [Hide]
       [State]: you have edited the value as text, but you have not set the fac
    Face used for widget buttons.
    Parent groups: [Widget Faces]
    Inherit attributes from these faces:
    [INS]
    Attributes of this face:
    [DEL] Weight: [Value Menu] bold
    [DEL] Foreground: black
    [Add attribute]

or 

    Widget Button Face: (sample) [Hide]
       [State]: you have edited the value as text, but you have not set the fac
    Face used for widget buttons.
    Parent groups: [Widget Faces]
    Inherit attributes from these faces:
    [INS]
    Attributes of this face:
    [DEL] Weight: [Value Menu] bold
    [DEL] Foreground: [Value Menu] *
    [Add attribute]

depending on whether we really need to be able to explicitly set the
"*" attribute value.

To implement this, we would need a new widget which was a mix between
the editable-list and the checklist widgets.  Or said in another way,
the new widget would be a compact form of the checklist widget, the
same way the menu-choice widget is a compact form of the
radio-button-choice widget.