Use energy deposition score for depletion

Introduce a new subclass of EnergyHelper, EnergyScoreHelper,
that computes the system energy using the energy-deposition score.
This energy is fed back to the Operator to normalize reaction rates.

The energy from the tally is only stored on the helper on the
MPI process 0 as to avoid scaling the system energy by the number
of processes. During the Operator unpacking, the energy reported
by each process is reduced, as the previous implementations took
fission reaction rates from the "local materials", e.g. the
materials each process is responsible for depleting.
The tally results are shared across all processes and only
contains a single quantity, the tallied energy deposition across
all materials.

This mode is controlled by passing the "energy_mode" argument passed
to the Operator. The two options are "fission-q" [default and previous
behavior] and "energy-deposition" [new features]. If energy_mode indicates using
the energy deposition score, the user-supplied fission-q dictionary is not used.

(cherry picked from commit d566f3080f)

docs/source/pythonapi/deplete.rst

@@ -95,6 +95,7 @@ total system energy.
    helpers.ChainFissionHelper
    helpers.ConstantFissionYieldHelper
    helpers.DirectReactionRateHelper
+   helpers.EnergyScoreHelper
    helpers.FissionYieldCutoffHelper
 
 The following classes are abstract classes that can be used to extend the