It’s time to rehabilitate Postmodernism. So at least is the contention of a new book by architectural historians Geraint Franklin and Elain Harwood that catalogs the great works of British PoMo in all their glossy splendor. Post-Modern Buildings in Britain, published by Batsford, is certainly a visual pleasure. It covers all the building types you’d expect, including cascading 1980s apartment blocks for yuppies, splashy office complexes that sought to embody their occupants’ power and wealth, an…