Add logarithmic color map mode

[nksauter]

It is hard to see the Bragg peak above the fuzzy diffuse halo. Perhaps there could be an option to allow a heat map to better portray steep pixel-to-pixel intensity changes. Activated by a keyboard shortcut?

[nksauter]

This is a longer term goal. Do not block development of the Methods in Enzymology release

[mewall]

@nksauter In addition to this issue of not seeing intensity that might be there at low level, it seems we are right now missing important information for understanding what we are seeing and diagnosing errors by not being able to see which pixels exceed the maximum value in the color map. I suggest a more immediate fix to address this specific issue by marking those pixels (e.g. making them yellow), and also displaying the threshold value used for the current rendering somewhere for the user.