Reviewed by Marina VaizeyTHAMES & HUDSON, 320pp, £35Tablet bookshop price £31.50            Tel 01420 592974 With its selection of some of the best, and best publicised, works of art of the past two decades, this book will provoke lively debate. The American poet and critic Kelly Grovier both tells and shows us the extraordinary sea change in how contemporary art is perceived, and how radically different it is from the work in the Western tradition that went before it. The choice of 100 works must have been agonising, considering the unprecedented explosion – in quantity if not obviously always in quality – of art since the 1950s. When I am asked to describe what has happened in art in the post-war period,