Fixes Gradients & Thicknesses:

1. Addresses existing broken special-casing for generic list parameter parsing
2. Adapts existing Gradients & Thickness special-cased conversion heuristics in Reservoir.py to work when parameters are provided as Gradients and Thicknesses (instead of Gradient 1–n/Thickness 1–n)
3. Adds example_multiple_gradients-2 example case which is identical to existing example_multiple_gradients example except the enumerated gradient/thickness params are given as their list-style equivalents