The work of JF has been supported by the Grant Agency of the Czech Technical
University in Prague, grant No. SGS15/215/OHK4/3T/14, and by the Grant 01-3-1116
of the Plenipotentiary of the Czech Republic at JINR, Dubna. He is also grateful to A
P Isaev and И Burdнk for discussions and support.
A part of this work, section 5, was performed in Steklov Mathematical Institute of
Russian Academy of Sciences by NAS and he was supported by the Russian Science
Foundation under grant 14-50-00005.
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