Today is the opening of the sale of the century at Bournes of Oxford Street. The sale will continue until the final item is cleared from the shelves and the store, a central London landmark since 1902, closes. The closure, the third by leading London department stores since last September is the latest in the melancholy litany of retailing institutions that have had their day and gone, leaving large freeholds behind like dinosaurs' bones. Those bones, in particula, are likely to have a brighter future with the approval by the last Great London Council last year of outline plans to turn the 'island' site into shops, offices and flats.