By Caldwell Titcomb April 1: Ursula Oppens, long a champion of contemporary music (and a 1965 honors graduate of Harvard), presents a free piano recital under the auspices of the Blodgett Distinguished Artists Series. The program includes John Corigliano’s “Winging It,” William Bolcom’s “Ballade,” Tobias Picker’s “Three Nocturnes,” the world premiere of Charles Wuorinen’s “Oros,”…