By Maria Tsvetkova and Steve Gutterman MOSCOW (Reuters) - The confession of a top dancer to plotting an attack on the artistic director of the Bolshoi Theatre's ballet company may not be the final twist in a scandal that has shocked Russia. The arrest of Pavel Dmitrichenko and two suspected accomplices over the January 17 attack on Sergei Filin has failed to put a lid on simmering tension and rivalries at the theatre, where there is talk of a wider conspiracy behind the scenes. ...