* Core bond yields, shares fall in European trading session* U.S. Federal Reserve statement due later* Key eurozone inflation gauge falls to new low* Short-lived rouble rebound after Finance Ministry sells FXBy Lionel LaurentLONDON, Dec 17 (Reuters) - Fears of a full-blown crisis in Russia and oil&aposs continued slide pushed investors to seek safety on Wednesday, buying core bonds and selling sto