Shortest path functions

[willGraham01]

We should write methods for the Connections class that handle some common network analysis tasks:

• Fetch the connections to/from a given node.
• Determine the shortest path between two nodes, by number of steps.
• Determine the "widest path" / "maximum bandwidth" path between two nodes.

For methods that return paths, we also need to have the option to return not just the "best", but a listing of all possible paths sorted in some order. As such, we also need to create "sorting" functions that can order the paths by a particular metric.