Implement Solution class for steady state simulations

[ma-sadeghi]

Currently, Solution object is only implemented for transient simulations.

[ma-sadeghi]

What added value does a SteadyStateSolution class provide? Is it just for consistency with transient algs?

[jgostick]

Yes, mostly for consistency, but there are perhaps features we'll add to the Solution class in the future which could be useful for both transient and steady-state. For instance, the solver convergence if interative, run times, etc.

[jgostick]

Also, for instance, see #2053. In fact, we also have the rate method on algorithms, which perhaps should be on the solution object, instead of the algorithm? Maybe?

[jgostick]

Also, it seems to me like the the conductance should be copied to the solution object, so there is a permanent record of the values in case they are changed on the physics object. Same for any reactions terms.