Adding travel time / weighted score based on terrain

[msradam]

When computing the distance from one site to another, we are also able to use iGraph to track the path from node to node in form of a list of edge IDs, which is how I was able to reduce the path (a list of IDs) to a list of distances (the length of each edge) to a final distance (sum of all lengths). However, since we have access to additional information about edges, we can also retrieve the type of road (walk, drive, highway, etc.) and determine a score or measure of travel of time based on that .