As cities go, Detroit does not have a good reputation. Decades of urban blight and civic mismanagement left the city in a hole which it has only recently begun to climb out of. But when the Detroit Symphony opens its new $60 million expansion of Orchestra Hall this week, it will represent the latest push by the community to revitalize the urban core. For the DSO, the project means a chance to continue playing downtown, and to do so in one of the finest performance complexes in the nation. For the project’s major benefactor, who admits that he was never much of a music fan, it means an opportunity to jumpstart the turnaround in one of Detroit’s most blighted neighborhoods.