We acknowledge the support of the Hungarian National Research Fund OTKA NN76727, CNK80991, T72954, K107228, the New Hungary Development Plan TA ḾOP-4.2.1/B-09/1/KMR-2010-0002, and the Swiss NSF and its NCCR MaNEP. E .K. acknowledges support of the Bolyai Jańos Scholarship of the Hungarian Academy of Sciences.