fixed grayscale issue s.t. bg pixels are drawn in lighter black-and-white
Changing variable name to match convention that I'm using in other im_hmi modules.
now have menu that reports fg/bg for locations on the IM
getting rid of extraneous use of self. in menu_handler
adding utility functions to compute pixels<->meters, used by bounding box and edit_pixel_labels
adding new Pixel message for the (u,v) coordinates in an image
im_hmi now allows labeling of pixels as fg/bg; minor cleanup of bounding_box code