Feature/galtonwatson

src/treex/galton_watson/__init__.py

+from treex.galton_watson.simulation import *
+from treex.galton_watson.identification_spinal_gw import *
+from treex.galton_watson.uglyduckling_spinal_gw import *
+from treex.galton_watson.most_likely_spine_spinal_gw import *
+from treex.galton_watson.average_spine_spinal_gw import *
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