update backprojection grass training image

[bsubei]

make sure there are no white lines or orange barrels. This training image should only have grass (the old one has white lines).

This should be a 5-minute task

[bsubei]

actually, turns out old training image doesn't have white lines. But it has orange barrels.

[bsubei]

I decided to make a node that goes through rosbags and calculates the histogram of all the frames (maybe add a skip config param) and then saves it to a yaml. This way, the line detection nodes that need to do histogram backprojection can just read in this training histogram and just keep using it. (perhaps this node can then be expanded to train more complex machine learning algorithms, but we'll see)

[bsubei]

histogram_calculator and backprojection nodes finished.