She shook up the male world of modern dance in the 1970s and never slowed down. The US choreographer talks about fending off flak, videoing her entire career " and why you should never ask her to 'dance a sunrise'The last time Twyla Tharp was working at the Royal Ballet it was 1995 and she was creating her comic Rossini ballet, Mr Worldly Wise. Now, as she returns, it's hard to recognise that two decades have passed.…