Add functionality to generate ion channel distribution metrics in models

[sanjayankur31]

In some models, where the distribution of ion channels may be dependent on some function of the distance from the soma etc., it'll be good to be able to:

• visualise the cell with the ion channel distribution
• get a graph of the conductance vs distance from soma

NEURON allows this as far as I know, and it should be possible for us to generate this too. Example: https://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1010506#sec022 (Supplementary figure 1).