IO handling between BT PortManager and Port Manager Interface

[maxsvetlik]

Proper IO handling system between bluetooth_port_manager and port_manager_interface, the latter being introduced by #8. While port_manager_interface acts as an intermediary between the Python library bluetooth_port_manager and the ROS nodes of serial_bridge, there is useful output from port_manager_interface that isn't logged by ROS due to the fact that it is printed directly to the console.