(initial) parameters for a new run. Three choices right now; from the
template itself, from the instance, or from the previous run. On the
web interface this is presented as three buttons. On ops, it is the
the -y option, which takes one of template,instance,lastrun as its
argument (you can of course combine the -y option with an XML file to
override specific params).

At present, there is no default. Lets give it a chance to sink in
before I pick something that will annoy 50% of the people 75% of the
time.