Updated pywidgets version to 4.2 to allow the notebooks to run.
Put import __future__ as the first line in each file to avoid
error stating that it must be the first line. Not sure when this
changed, it worked before.
I added titles so you can see where in the processing the
graph is.
This surfaced a bug in matplotlib 1.5 (#5399) so I added
some code to work around that.