HAPPENIN’ OTSEGO for THURSDAY, DECEMBER 20 Piano Sing-A-Long At History Center PIANO CONCERT – 6 – 8 p.m. Sing-a-long to player piano performing holiday carols, other favorites. Includes seasonal refreshments. Oneonta History Center, 183 Main St., Oneonta. 607-432-0960 or visit www.oneontahistory.org…