[Enh] Spatially explicit variance-based sensitivity analysis

[JusteRaimbault]

Implement spatially explicit variance-based SA
see Ligmann-Zielinska, A. (2013). Spatially-explicit sensitivity analysis of an agent-based model of land use change. International Journal of Geographical Information Science, 27(9), 1764-1781.

[JusteRaimbault]

additive random perturbations, relevant for Gaussian multivariate fields
Angulo, J. M., & Bueso, M. C. (2001). Random perturbation methods applied to multivariate spatial sampling design. Environmetrics, 12(7), 631-646.