This is useful for adding 'cursor-face or 'mouse-face to each row.  I've
been advising 'vtable--insert-line' with an after advice.  This is better.

Example:

          (make-vtable
           :columns
           '(( :name "Foo"
               :primary ascending
               ))
           :allow-other-keys t ; backward compatibility for :row-properties
           :row-properties '( mouse-face highlight
                              cursor-face region)

-Stephane