[GeraultTr]

Hello @rbarillot,
In the perspective to have tillers and their nodal roots' subset as progressively plant subparts, needed to add the possibility to explicitly simulate tillers, independently of Main Stem's functioning.

This requiered heavy edits on the model and simulation files of each model, so an expert review is surely needed to check I did not forget something ;)

For now, until I wire each axis' xylem and phloem to specific root subsets, we still use Main Stem's xylem and phloem as unique and homogeneous plant pools.

(@pradal might help to converge with hydroroot as well)