Reuse Previously-Computed Interpolation Surrogate Points

[pbauman]

It would be nice to be able to just supply the data file and have those points reused when running a new surrogate. Uniform refinement is the obvious case, but even more generally, just integrating those points into the newly generated points would be nice. Crux would be inserting the "node" in the proper place in the arbitrary dimension structured grid.

Won't have time to do this for awhile, but at least wanted to log it in case someone wants to pick it up and do it.