By Denny Dyroff, Staff Writer, The Times   The Philadelphia Museum of Art sets the backdrop for the annual Welcome America fireworks display. Independence Day has arrived and that means it is time for two of Chester County’s longest-running and most popular Fourth of July events — Downingtown Good Neighbor Day (Kerr Park, Downingtown, 610-285-1119, www.goodneighborday.com) and Freedom...