The GridHelper is an object to define grids. Grids are two-dimensional arrays of lines.
size -- The size of the grid
step -- The size of the step between 2 lines
colorCenterLine -- The color of the centerline. This can be a
Color, a hexadecimal value and an CSS-Color name. Default is 0x444444
colorGrid -- The color of the lines of the grid. This can be a
Color, a hexadecimal value and an CSS-Color name. Default is 0x888888
Creates a new GridHelper of size 'size' and with steps of size 'step'. Colors are optional.