Add option to display coordinate space indicators (axes or floor, for example)

[a2sheppy]

It would be really helpful for the purpose of debugging certain types of failures involving matrix math errors and other data or computational errors if we could toggle on options to do things like:

• Render the axes (x/y/z) for the world's coordinate system
• Draw the world's floor as a simple translucent square
• Render the axes for any given pose(s)
• Draw the world's floor as a translucent square with grid markings to show distances
• Possibly similar plane options for the other directions (vertical parallel to the Z axis and the X axis)
• Draw a 3D grid of faint lines or of dots to help judge distances or positions

Any one of these would be really helpful; having more than one would be spectacular. Just having either of the first two items would help me solve an ongoing bug I've been hunting for days now..