The Maextro S800 wants very badly to be a Rolls-Royce.At 18 feet long, painted two-tone, lined with soft leather, backed by Huawei and built by a thousand robots in Hefei, it has the size and the price tag of ambition. What it lacks is the one thing Rolls-Royce has spent a century perfecting: restraint.A car that can park itself is a clever feat of engineering; most Rolls-Royce owners employ a driver for that.The Maextro comes with a 40-inch scr…