By Martin Baccardax A harsh series of weekend sanctions has markets in retreat around the world Monday, with ruble plunging to an all-time low against the U.S. dollar. U.S. equity futures slumped lower Monday, while oil prices tested fresh 2014 highs amid a broader rally in commodities prices, as fighting between Russia and the Ukraine entered its fifth day and western world leaders moved to isolate Moscow from the global financial system. Russia’s central bank was effectively blocked from accessing hundreds of billions of U.S. dollars stocked away to help defend its currency, with the ruble l…