One of my favorite “Downtown Abbey” characters is Cora, Countess of Grantham, played by Elizabeth McGovern.  She is an American heiress whose marriage to a titled but cash-poor nobleman resulted in the most unexpected of romances.  The producers announced this week that Season Three will include a visit from Lady Grantham’s American mother — and that she will be played by Oscar-winner Shirley Maclaine.  I can already imagine the fun of seeing a strong-willed nouveau riche American going up against the Dowager Countess, played by Oscar-winner Maggie Smith.