Add a Grid Overlay to Map

[Notgnoshi]

On simple simulations with no obstacles, it can be quite hard to get a good sense of how your robot is moving, and at what scale.

I would like to have a grid overlay for the purpose of having something fixed to track the movement of my robots relative to. It would also be nice to see the coordinates of the cursor displayed somewhere like the taskbar. See this Gimp screenshot:

I've taken to drawing dots on my screen with a dry erase marker as a reference to tell if my robot is driving in the intended path.