Oberon reaches near-Bowie levels of magnificence in a feather-fringed fur coat, PVC trousers and glam rock makeup; Tytania shimmers in a pink evening gown and boa worthy of any cabaret diva. Trinity Laban’s 1970s A Midsummer Night’s Dream takes Britten to the disco – and back again. Cordelia Chisholm’s clean, hard set, made luscious with…