GLOBAL MARKETS-Stocks rise on upbeat U.S. data, euro falls

* Robust U.S. retail data rekindle some bids for stocks * Ukraine's ultimatum to separatists saps risk appetite earlier * Euro undermined by ECB officials' talk of more easing * Japan's Nikkei marks fresh 6-month closing low (Updates market action, adds quote) By Marc Jones LONDON, April 14 (Reuters) - Global equities rose on Monday on robust U.S. retail sales data, rebounding from last week's steep decline, while the euro fell, prompted by the European Central Bank's stron