Ctrl + C kills spawned GUI when launched from shell

[bennuttall]

When the GUI is automatically spawned from a Python shell, any keyboard interrupt will silently kill the GUI.

To reproduce:

1. Open a Python shell

2. Import sense_emu and create a SenseHat object:

   from sense_emu import SenseHat
   sense = SenseHat()

   (A GUI will be spawned automatically)

3. Run a while loop, e.g:

   while True:
       print(1)

4. Hit Ctrl + C to terminate the loop

5. Try to update the Sense Hat display:

   sense.clear(255, 0, 0)

   (the LEDs on the display should go red, but they don't)

6. Re-initialise the GUI:

   sense = SenseHat()

   (note the leds are now red)

7. Try to update the display again:

   sense.clear()

   (this should (and does) clear the leds)

It seems that killing the while loop also kills the GUI process spawned from the shell.

[waveform80]

This is because signals are sent to the process group on Linux/UNIX (and Windows? Not sure). Easy enough to fix with setpgrp - I'll push something in a mo.