This DCist thinks the National Building Museum is unsung. It is the most amazing space in this fair city (in the gigantic red-brick Montgomery Meigs-built old Pensions Building) and the exhibits are not run of the mill. Who knew concrete could be interesting? The museum’s latest show, “Jewish Washington: Scrapbook of an American Community,” is really a classic immigrant story: Jews get persecuted in other countries, come to the U.S. and D.C. for a…