Initialize plasticity properties and associated initial stress quadrature points wise

[Thomas-Ulrich]

Plasticity properties and associated initial stress are initialized element-wise.
It would make sense to initialize them (at least the stress) quadrature point-wise given that plasticity is evaluated at the quadrature points).
(I'm just pinning that here to remember. I realized they are initialized element-wise when reading the homogenization PR (#644).