Basic label setting algorithm for MOSPP

[PatrickOHara]

Is your feature request related to a problem? Please describe.

Implement the basic label settings algorithm for MOSPP from Martin's paper. This algorithm will be slow but we can make improvements on top.

Describe the solution you'd like

• [ ] Split the algorithm into several functions
• [ ] Define the data structure for a single Label. Should this be a class or some other DS?
• [ ] Build a priority queue of labels.
• [ ] Maintain a list of labels on each node.

Describe alternatives you've considered

We could implement the A* variant, but this is a natural extension of the basic algorithm.

Additional context

See the Martin's paper in overleaf doc.

[PatrickOHara]

Oops just seen you've already started a PR for this @JamesCraster ! I'll close this as duplicate