Improve lookup algorithm in areas plugin

[Major-]

The area plugin currently stores all of its entries in a Set, which is then iterated over. As this occurs for every movement update, we should really optimise this to some sort of location-aware data structure - probably a quadtree, but there might be alternatives.

[rmcmk]

Quadtree sounds best, I think. Any other ideas on this topic?

[Tomm0017]

Unrelated - If we want to improve the lookup, I personally believe that using 8x8 tile areas would be best as it would trigger the event 1-7x less frequently than it does currently. I'm pretty confident that RS uses 8x8 chunks for everything, so there shouldn't be a case where you need to specify an area that can't be made up of 8x8 chunks.