THE COVER PICTURE on this year's town report is of one of the most elegant of  the Georgian architecture  practiced in America in the early homes in the Connecticut Valley, built by Alexander Field  in  1794.  It is a variation late 18th and early 19th centuries.  The measurements of its beautiful proportions are on file in the Library of Congress and it has long been the subject of attention by students of American architecture.   The present owners are Mr. and Mrs. Jacob Richmond, who have done much to restore this exceptional house to its original style and beauty.  The painting is by Arthur A. Hart, Chairman of the Art Department at Bay Path Junior College.