IT’S TAKEN ME A LONG TIME TO FIGURE OUT WHAT TO SAY about Big Dance Theater’s Supernatural Wife (based on Anne Carson’s translation of Euripides’s Alkestis), a new commission recently on stage at the Walker. The show’s well-crafted, fast-paced, hipper than we knew we could be and yet never difficult to follow — in short, so deafeningly contemporary it’s hard to see ‘round it. But I think I can make…