Change polygon storage to DCEL

[jtoumey]

Use a more appropriate data structure for storing the polygon.

• https://w3.cs.jmu.edu/bowersjc/page/courses/spring17/cs480/labs/dcel/
• http://www.flipcode.com/archives/The_Half-Edge_Data_Structure.shtml
• https://cs184.eecs.berkeley.edu/article/12
• http://www.cs.sfu.ca/~binay/813.2011/DCEL.pdf
• https://cs.stackexchange.com/questions/2450/how-do-i-construct-a-doubly-connected-edge-list-given-a-set-of-line-segments

[jtoumey]

Also, the quadtree will eventually need point coordinates from the polygon to appropriately immerse the boundaries.