[TRM] An option to avoid the initial total stress deduced displacement.

An option to avoid the initial total stress deduced displacement. With this option being on, the displacement unknowns are obtained by solving the following momentum balance equation:

\nabla \cdot (\mathbf{\sigma}-\mathbf{\sigma}_0)+\mathbf{f}-\mathbf{f}_0=\mathbf{0}

with \mathbf{\sigma}_0 the initial total stress.

Note: If this option is set on, the option of compensate_non_equilibrium_initial_residuum must be set off. Vice versa. compensate_non_equilibrium_initial_residuum includes the non equilibrium initial residuum of the pressure and the temperature parts, which are unnecessary for most of applications.

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2. Tests covering your feature were added?
3. Any new feature or behavior change was documented?