[CM] Snd GUI changes

[Bill Schottstaedt]

I've made several changes to the Snd GUI lately, mostly
incorporating Dave Phillip's suggestions from long ago,
and continuing the struggle with gtk3/cairo.  If any cmdister
is interested in this business, please send me any ideas!
GUIs are not my strong suit.  The CVS sources/daily tarball have
the latest stuff, and there's a disheartening TODO list toward
the end of snd-gutils.c.