“The great contralto used to live in this two-story house at No. 762 on South Martin Street, now known as Marian Anderson Way. She entertained in the basement during those inhospitable years of segregation when she feared what unkind words might ricochet her way in the city’s downtown eateries. … [H]ere, on a quiet street in South Philly, you can get a feel for the life she lived and the family she came from.”