SERIES PREMIERE: Game of Thrones has done so well with HBO, drawing viewers as well as earning acclaim and Emmys, that it’s no surprise that rival networks and TV producers are seeking to mount similar costume dramas set in centuries long ago. FX’s The Bastard Executioner, this season, is one, and now here’s another. It’s a British import set in the mid-800s. And no, I didn’t drop a numeral there. This is another Vikings saga, this time from the British point