The new class method ResultsList.from_hdf5 should be
used to load in results data, rather than passing
the file name into the __init__ method. __init__
passes directly to list.__init__ now.
The motivation for this is to resolve the depletion
restart with MPI bug #1275. To do this, each Operator
will create it's own ResultsList and distribute reaction
rates and densities according to what materials are burned
on this process. Rather than use a normal list, this Operator
expects the various accessor methods like get_atoms to be
present on self.prev_res
