start adding statistics for broker

broker/src/hidra2_broker/database/database_test.go

broker/src/hidra2_broker/database/mock_database.go

broker/src/hidra2_broker/server/get_next.go

broker/src/hidra2_broker/server/get_next_test.go

broker/src/hidra2_broker/server/server.go

broker/src/hidra2_broker/server/server_nottested.go

broker/src/hidra2_broker/server/statistics.go

broker/src/hidra2_broker/server/statistics_test.go

broker/src/hidra2_broker/server/statistics_writer.go