To enable those that are using taskflow to easily attach
to an engine (say in a unit test) and capture all the transitions,
details and state changes in a accumulating 'values' list provide
a capturing listener that does just this (and change the one used
for internal testing to use it) so that others may also benefit
from the same functionality.
Change-Id: I7a35e282dd4a6b3e14277bea2af1f275615bd212