Most of this week looks sleepy as far as classical music goes. However, by the end of the week, there will be three events, all of which are high on our December list and all happening simultaneously. How to choose? SUNDAY, SUNDAY, SUNDAY: >> Wagnerian tenor Ben Heppner is scheduled to give a recital on Sunday afternoon (December 2, 5:30 p.m.) at Baltimore's Shriver Hall. It will be Heppner's first appearance in Baltimore and his......