Explore region-of-interest limits for image binning (and histograms?)

Now that the image binning tool `images` runs on Dask, it ought to be straightforward to allow the user to specify a region of interest from which to include events, disregarding all others. This would allow investigation of the evolution of a single stationary diffraction peak for example. It might also be useful to apply the same ROI limits to a time-histogram tool (see #21).