“Oh cold, cold, rigid, dreadful Death, set up thine altar here, and dress it with such terrors as thou hast at thy command,” says Ebenezer Scrooge near the end of Charles Dicken’s A Christmas Carol. That’s exactly what Karl Toomey did for the Lifelogging exhibit at the Science Gallery Dublin. In a show concerned with “exploring new ways to track everything,” the piece that has so far garnered the most attention is a gravestone belonging to the fictional Kurt Mark O’Neill.    Born at the turn of the century and dead sixty five years later, O’Neill had 672 Twitter followers,…