Debugged the status transmission.

Note: the status tab is now refreshed using the received data, but
      the read buffer must be cleared first by unplugging the serial
      adapter.

-SerialPortListener:
    Moved the QSerialPort object declaration to the thread itself.
    Fixed unsigned to signed casts.

-StatusTab:
    Fixed the 'refresh' slot, especially the status bitfield manipulation.
Merge branch 'serial_port_listener_qthread'