Quadtree for large scene optimization

#algorithm #wip References:

• https://thoughtbot.com/blog/how-to-handle-large-amounts-of-data-on-maps
• https://www.phase2technology.com/blog/using-d3-quadtrees
• https://freecontent.manning.com/wp-content/uploads/optimizing-xy-data-selection-with-quadtrees.pdf
• https://d3-wiki.readthedocs.io/zh_CN/master/Quadtree-Geom/
• https://bl.ocks.org/mbostock/4343214

Main idea: Use [Quadtree] to maintain a visible window of a much larger scene, everything staying outside that window can be off-loaded in some manner, to save computation time and memory.