Open the specified instance.
A derived class looks for the instance, and if the instance already has
open tableaux, then put those in the foreground
Otherwise, create a new tableau and if
necessary, a new effigy. Unless there is a more natural container
for the effigy (e.g. it is a hierarchical model), then if a new
effigy is created, it is put into the directory of the configuration.
Any new tableau created will be contained by that effigy.