PARIS — Ex-trader Jerome Kerviel was convicted on all counts today in history's biggest rogue trading scandal, sentenced to at least three years in prison and ordered to pay his former employer damages of €4.9 billion ($6.7 billion) — a sum so staggering it drew gasps in the courtroom. The court rejected defense arguments that the 33-year-old trader was a scapegoat for a financial system gone haywire with greed and the pursuit of profit at any cost — a decision sure to take some pressure off the beleaguered banking system overall. By ordering a tough sentence for a lone trader,...