Make the lights adjustable in a race via the debug menu

This makes it possible to adjust energy, radius and color of the lights while being in a race. For simplicity, only the light nearest to the player kart is edited. The current solution isn't the most elegant, but it should be possible to work with it.

@samuncle what should be the ranges for the values for energy, radius and the colors of a light? And how many steps should be between minimum and maximum? Currently, the ranges are just my try-and-error assumptions.

todos:
 - Better handling of the SpinnerWidget's
 - Make the values changable via mouse (clicking somewhere in the spinner) oder via keyboard
 - Ability to select a different light? Maybe with a GUI where the selected light changes the color.