By Alexander Hübner and Elvira Pollina BERLIN/MILAN (Reuters) -ProSiebenSat.1 said on Monday that MediaForEurope (MFE) had rejected the offer of a seat on the supervisory board of the German broadcaster, suggesting that no compromise has been reached with its top investor ahead of a May shareholder vote. MFE, which is controlled by the family of former Italian Prime Minister Silvio Berlusconi, has called for closer cooperation with Munich-based ProSieben, in which it has a voting stake of more than 25%. The Milan-listed group has also asked ProSieben to engage in talks over strategy, focusing …