Tupek/differentiable block solver

[tupek2]

A few ongoing fixes and improvements

• Add differentiable block solver. This block solver uses block linear solvers, but otherwise calls our existing nonlinear solver (e.g., Newton) over the entirely block system. This allows monolithic nonlinear solves.
• Remove duplication in test_solid_mechanics_state_advancer
• Initial version of test_thermo_mechanics.cpp a coupled test that uses the new FieldStore as a prototyp
• Update to latest gretl, which fixes an asan issue and also improves performance in some cases
• Change the default NewtonLinesearch to use 10 cutbacks. Small interface changes around this to ensure Newton still defaults back to 0 cutbacks.
• Taylor series style for residual update in warm-start to better handle physics which start out of equilibrium