[THM] rename storage

Replace storage by storage model derived from fluid compressibility and solid grain compressibility. Most benchmarks are not affected as they used storage=0. The benchmarks for anisotropic thermal expansively used a storage term to achieve convergence but only their strain solution was checked analytically. However, pressure and stress solutions deviate inevitably -> new testing files for anisotropic thermal expansion.

1. Feature description was added to the changelog
2. Tests covering your feature were added?
3. Any new feature or behavior change was documented?