Added itemKey property to probes.

Probes now have both a key and an index for their associated synset
Added the key so that when we create the graph, we can use the key
instead of the index in the legend since keys are more informative.
Added maxInvalidMatch stat.

Added the maxInvalidMatch statistic, basically the maximum match from
all synsets that are not legitimate matches.

Also, made the criterion for correctness more consistent, using
maxInvalidMatch.
Made graphs savable, fixed jump planning.

* Fixed jump planning, so we can specify keys and relation indices
in run_script, and these will be the links that get tested in the
jump test

* Made it so graphs are saved, and so that matplotlib is imported
conditionally
Updated log.