Several months ago I wrote about ventilation hoods, calling them the "afterthought" of kitchen appliances. This column deals with the bathroom equivalent – medicine cabinets. How many times have you settled for the antiseptic white, recessed box with chrome trim around the mirror? Or a surface-mounted mirror and the shallow cabinet with the sliding Lucite doors? It's as though manufacturers, designers, and contractors have collectively and perversely tried to provide and install the most insipid collection of medicine cabinets imaginable. But the explosion of beautiful bath materials, fixtures, and fittings has made the old standard in medicine cabinets look shabbily out of place. Upscale customers no longer will settle for a $50 medicine cabinet astride their $1,000 Sherle Wagner sink or