Increase stress field coupling

[simopier]

Reason

Add a stress-field coupling by adding one additional term to the mobile-diffusion in the foster-mcnabb equations. There are a number of papers on this (see the Sofronis and McKeeking blunting crack tip)

Design

Couple tritium transport capabilities with stress-field, and document how to set such a simulation up.

Impact

Enhance capabilities for transport by accounting the effect of stress, and better inform users how to use these capabilities.

Suggested by @stephen-dixon