The work was supported by grants RFBR 13-01-00251, 05-01-01119, 13-01-12462, State contract no. 8223 'Dynamic instability and catastrophe' (RF) and RF Program for the State Support of Leading Scientific Schools NSh-2964.2014.1.
Поступила в редакцию: 01.09.2014 Принята в печать: 18.03.2015