Completed the J mag histogram for proto/disk/nodisks.

Next step: abstracting it so I can have four more for free!
Now I make five histograms with mostly-the-same code!

J, H, K, J-H, H-K. It's great!

Next: have the plots say the medians.
Added lines to show the median delta mag/color for each subplot.

I think I'm done with this subtask for now!