By Christoph Steitz and Tom Käckenhoff FRANKFURT (Reuters) -Germany’s Uniper remains in talks with Gazprom and the German government over how to implement Moscow’s demand to pay for Russian gas in roubles, which the European Commission said would breach sanctions. Uniper, in presentation slides published along with final first-quarter results, cited “ongoing discussions with German government and Gazprom on potential implementation” of the decree, which has stoked fears that supplies may be disrupted. The company, Germany’s largest importer of Russian gas in which Finland’s Fortum owns 78%, de…