Adjust includes according to iwyu

include/linkahead/authentication.h

include/linkahead/configuration.h

include/linkahead/entity.h

...de/linkahead/file_transmission/download_request_handler.h

include/linkahead/result_set.h

include/linkahead/result_table.h

include/linkahead/transaction.h

src/linkahead/authentication.cpp

src/linkahead/configuration.cpp

src/linkahead/file_transmission/download_request_handler.cpp

src/linkahead/logging.cpp

src/linkahead/result_table.cpp

src/linkahead/status_code_description.cpp

src/linkahead/transaction.cpp

src/linkahead/transaction_handler.cpp

test/test_clinkahead.cpp

test/test_configuration.cpp

test/test_connection.cpp

test/test_data_type.cpp

test/test_entity.cpp