Northern Ireland now takes up the challenge of Mastermind. Its four contenders are meeting tonight at the Civic Centre in Newcastle upon Tyne. They are:John Campbell (travel agent): 19th-century inventionsHarry Irwin (representative): British cartoons and cartoonists 1930-1980Margaret McNulty (undergraduate): Kings and Queens of Britain 1485-present dayTony Veitch (civil servant): Life and works of A. E. Housman