This helps later archaeology

I know this is kind of naughty, but this is one of the #1 failure modes right now.

Also, add progress bar.

Lists of counts had pervaded every corner of CrystFEL, being used as markers
for the presence of reflections.  Now we have a better way of doing this,
the ReflItemList, and few parts of the suite apart from process_hkl have any
business knowing how many observations were made of a particular reflection.