The â??artistâ??s museâ?* is unfashionable now, but she was the making of Alex Katz. As a young artist in 1950s New York, Katz didnâ??t know how best to paint. He tried collages and landscapes, without much interest or success; he watched de Koonings and Lichtensteins flourish, but wasnâ??t drawn to their novel styles. Then, in …