implement class serializer in network

issue #189
Implementation feature create_server and close_server of class SUDOKU_SERVER

issue #190
Implementation feature connect and disconnect_client of class SUDOKU_CLIENT

issue #191
Add class sudoku_test_net_client and tests

issue #192
Add class sudoku_test_net_server and tests

issue #192
Add class sudoku_test_net and tests

issue #192
Merge remote-tracking branch 'origin/Network'