pathfinding: optimizations

[d4l3k]

Optimizations:

• Avoid doing lots of Point to ID conversions by keeping a map of ID to node and not storing Points in the PriorityQueue.
• Avoid overhead from using the typescript-collections Set implementation and instead just use a JS object.
• Avoid deoptimizations in JS due to different Point classes by copying the start and end points.
• More efficient Point to ID conversion by not using JSON.stringify.

JS profile differences start (32.22%) / finish (4.93%): http://imgur.com/a/wefuC