(Classical music agenda contributed by Charles T. Downey of Ionarts) Want to hear something classical to impress your family and friends? At DCist, we have some quick picks for you, and can you say free concerts? That’s right, Washington has more excellent classical music to be heard for free than probably anywhere else, and we’re here to tell you about it. For more information, see our Concert Schedule at Ionarts. LIBRARY OF CONGRESS: >> Free…