Python bindings: Add license headers to all files

python/py_block.cpp

python/py_block_table.cpp

python/py_cdns.cpp

python/py_cdns_decoder.cpp

python/py_cdns_encoder.cpp

python/py_common.h

python/py_dns.cpp

python/py_file_preamble.cpp

python/py_format_specification.cpp

python/py_interface.cpp

python/py_timestamp.cpp

python/py_writer.cpp

python/pycdns.cpp