MaterialHyperElastoPlastic1 -> need for History Fields?

The plastic material tests made the need for a state field, or history
field, abstraction apparent. Such a field represents the current new,
as well as the previous n values of a field. The iterator maps over
this field then give const ref access to historic values while giving
ref access to the new (or trial) state. An "increment" method then
cycles the new state to old, old to old-1, etc, by relabelling rather
than copying the data.