Scale network graph edges by 'connectivity strength' between 2 nodes

[thundergolfer]

Description

We want to somehow communicate how closely to members work. ie. their level of collaboration.

This can be set by a function on the width of a graph edge, according to some value which represents the level of collaboration.

Note: see issue #33 for info on how to measure level of collaboration

Basic implementation direction

This will be implemented as javascript, as a function used in the D3.js graph building.