Access scorer functionality from Python

[ajasja]

Expose the scorer classes (ScoringHelper etc...) to Python.
Either using pybind11, Boost.python or SWIG.

[dancsi]

Work for this has started in 86bb6b8. Now, the pyccscore module is copied to the install directory, and can be imported as a regular module. It provides the functions score_potapov, score_bcipa and score_qcipa.