In the week that Doris' crack gets filled in, Tate Modern has announced plans for a rethink of the building's river-facing facade. Between May and August, a group of the world's most acclaimed street artists will be allowed to daub their designs across designated 15x12 metre areas on the north side of the former power station, the first time the exterior has been used in such a way. According to curator Cedar Lewisohn, the......