Allow using list-colors-display to set colors in the Color widget.

Allow using list-colors-display to set colors in the Color widget.

* facemenu.el (list-colors-display, list-colors-print): New arg
callback.  Use it to allow selecting colors.

* wid-edit.el (widget-image-insert): Insert image prop even if the
current display is non-graphic.
(widget-field-value-set): New fun.
(editable-field): Use it.
(widget-field-value-get): Clean up unused var.
(widget-color-value-create, widget-color--choose-action): New
funs.  Allow using list-colors-display to choose color.