-Renamed NSSlider size to gridSize (more explicit) and added a pencilSize NSSlider
-Added ad new feature and two need sliders : extended mouseDown: so that we simulate a square pencil of size 1+-pencilSize/2 which has an evenly distributed probability of value pencilDensity to toggle a cell inside the pencil radius. This is way more relevant that a single cell toggling like in was implementing since these medium size structure can actually propagate and interfere with current patterns (which a single cell alone can’t do).
This give ways to interact by impulse.