Visualize Reference Frame

Add a reference frame visualization using r/g/b to represent the x/y/z.

This function adds a reference frame a specified parent or the current axes using red/green/blue to represent the x, y, and z-directions respectively. An hgtransform object is returned that is the parent of three line objects representing the specified axes. A number of parameters can be varied allowing the user to adjust the reference frame representation as needed.