New totals implementation.
Currently we have routines which add up values for the whole root system. These are typically based on nested objects and walking through the object tree. They are slow and create a lot of overhead. The alternative is to implement them more similar like doussan code, which registers a hook for the formation of any root node, and keeps a pointer list to all the nodes it wants to add up.
Note that adding up may have an easy alternative that allows to integrate over root length or surface area (etc). We could gain here some precision and would not have to do this integration in the rootSegment"xxxx" routines.