Soil-abiotic links review

All the links we want between the abiotic models (microclimate and hydrology) and the decay models (soil and litter) have now been implemented (at least for `v1.0.0`). A final thing we should do before initial release is to check that all of these links are (a) correct and (b) passing the information in the most useful form.

There's already a few issues that fall under this umbrella (#533, #535, #346), but I think there would be a real value in sitting down and going through the whole model flow systematically to check that everything makes sense.