Simple demo for the GUI tool. Upon running the script ./start,
a cart-pole plant is launched. The torque applied to the cart
can be adjusted with the slider in the GUI tool.

KNOWN ISSUES:
On some systems, the QT-Slider widget does not function
properly, but keeps snapping to certain values. There is
no known fix for this at present, though the issue can
be worked around to some degree by changing the values
in the parameter gui_request_string in cartpole_gui.cls,
which should cause different locking positions.
