Save enthalpy discrepancy in matching list file.
Only try making png's for inline display for IPython console front ends.

If you had IPython, but were not running in a console that rendered png's,
then you would end up with the text __repr__ instead of nothing, polluting
your console output.  This is perhaps slow (making pngs that are not displayed)
and should be revisited, but is a temporary fix.
Keep track of which edge reactions need re-checking.

This should avoid the "check absolutely everything" when you run low on
species. When you match a species, you need to re-check the reactions
that it is involved in, in case you can learn anything new from them.