The SpdPythia8Generator update.

Now SpdPythia8Generator is now inherited from SpdGenerator, which should
    -- avoid potential problems with some SpdPrimaryGenerator calls,
    -- save generated particles, that we not passed to Geant4.

Now the seed for Pyhthia is set manually like in "macro/SimuPyth8Hyb.C".
We can decide latter if it resonable to take it from gRandom (the code
can be uncommented).