add solid water data

[nbassler]

• public datasheet for SW HE: https://www.sunnuclear.com/uploads/documents/datasheets/SolidWaterHE-TMM_110420.pdf but elemental composition is absent. For older version of SW there is: https://doi.org/10.1088/0031-9155/59/1/83

which has maybe good enough for a start