Improved serial port communication.
** Moved worked thread and added new serial RX thread to
   prgexec.py (new file).
** Added new global event for serial rx data.
** All serial output now goes trough thread.
** Receive serial data is only from serial RX thread.
** Using pySerial read() api instead of readline.
** Changed all gcs to gsat name sapace.
** Added appropriate GPL2 copyright to all .py files.