Added Keff Search wrapper to python API
Created by: nelsonag
This PR adds a python API class to perform keff searches given changes in a single parameter. This is written generically so that its major input includes some function which builds the model and returns a set of input classes inside a new container object also included in this PR,
A new notebook is included which shows this off via a critical boron search of a pin cell problem. I've also used this to re-create the LA-10860-MS simple critical slurry cases.