Fix #36: remaining icons: undead, signpost.

I consider the creatures on undead's buttons a sensible exception to the monochrome-buttons thing. I think it would be more distracting to have them differ from what's in play.

Also change asterisk to 123.

The signpost left/right and the 123 are the parts of all this I'm least sure about; they're definitely improvements over letters / mouse analogies; further improvements welcome. :-)