GLOBAL MARKETS-China shares plunge, Europe eyes crunch ECB meeting

* Chinese shares plunge 7.7 percent* Europe gears up for ECB, Greek election* Bond yields hit new lowsBy Jamie McGeeverLONDON, Jan 19 (Reuters) - Chinese shares chalked up their biggest one-day slide in nearly seven years on Monday after regulators there took steps to rein in speculative lending, while investors everywhere braced for what is shaping up to be a critical week in the euro zone.Expect