SEAVEA release

Overhaul of SC sampler / analysis class:

• Made isotropic sparse-grid subroutines more scalable to higher input dimensions. Reused dimension-adaptive subroutines for this purpose, instead of having (slower) separate isotropic routines.
• Rewrote dimension-adaptive SC expansion as a standard PCE expansion with generalized PCE coefficients. See adaptive sparse-grid tutorial.

Documentation:

• Extensive methodological sparse-grid tutorial: https://www.researchgate.net/publication/359296270_Adaptive_sparse-grid_tutorial
• New tutorial on using mathematical expressions involving parameters in template files using the Jinja encoder: https://github.com/UCL-CCS/EasyVVUQ/blob/dev/tutorials/jinja_tutorial.ipynb