Refactor split_link() and move to geo utils

Requested by @e-lo in PR #408 

https://github.com/network-wrangler/network_wrangler/blob/main/network_wrangler/utils/geo.py

Also suggested: 

> It seems like it would make sense to encapsulate this whole thing in a funct and call it once on forward and once on reverse. As it is it is really verbose.

There are some other TODOs issues related to this method as well.