adding first pass at geocoding all the marta stations
implementing geolocation check for nearest station

- prompts user for permission
- if they accept, we get their approx location
- we calculate their nearest station from hardcoded list of coordinates
  (may need some QAing to make sure these coordinates are accurate)
- after receiving list of arrivals from backend, we cross-reference their
  nearest station and the list of arrivals
- if a match is found, we show it at the top of the main list