By Denny Dyroff, Entertainment Editor, The Times Vicki Peterson and John Cowsill On February 24, the Sellersville Theater (24 West Temple Avenue, Sellersville, 215-257-5808, www.st94.com) will host a music act that spans pop/rock generations – a popular band that shone in the late 1960s and a group that was one of the hitmakers in the 1980s. On Tuesday night, the duo featuring Vicki Peterson...