waterfall.set_lookup_levels mods

Main change is the addition and connecting of set_lookup_levels to get the color scaling limits synchronized with the plot.
dlog() was never intended to be a permanent/expected feature at all, so I
was not worried about other developers' expectations.  It was temporary
during my active/current development.  They are only in the commit still
because there is remaining debug work that needs logging and deleting them
is more annoying than disabling.  If it were "done", you would never have
seen dlog!

For my own quick debugging I would definitely not use logging, so I
didn't.  Next commit I'll just yank my very selective/sporadic dlog
statements entirely before commit so that they don't contaminate the pyrf
repo. I wasn't considering release to github as a requiring removal of
temporary stuff like that... but I think I have underestimated the release
requirements for the repo.  I'll keep and track that cruft separately next
time... sorry.