For the next work on my list of the 50 best/most important/most interesting paintings in and around Boston, I head about 20 miles north to the Addison Gallery of American Art at Phillips Academy in Andover. Completed in 1928, “Manhattan Bridge Loop” is one of Edward Hopper’s largest paintings, about the same size as “Nighthawks” and “Early Sunday Morning.” And it might also be one of his most enigmatic. On the one hand it’s a beautiful, quiet portrait of New York City. The ab