Convert SA server to use iterative-statistics library

This MR aims to convert Melissa from using our own iterative statistics methods to outsourcing to Iterative Stats.

During this PR I raised an associated PR in the BasicIterativeStats which, if approved by Frederique, would allow us to remove the StatisticalMoment class definition from our source.

• Convert Sobol methods
• Convert Statistical Moments
• Convert experimental design to Iterative stats library methods?
• Add checkpointing
• Add documentation helping a user understand experimental design, and how they could customize our experimental classes
• Convert DL parameter generation to new experimental design API