Add route to map when click 'Get Directions'

* Creates a DirectionsView that implements a Google Maps
  DirectionsRenderer
  [Directions Service](https://developers.google.com/maps/documentation/javascript/directions)
* Takes the current destination and displays a route to the marker
  that was clicked

Next Steps:
* The renderer creates a new pin that's in a slightly different
  location from the original pin. Will either need to hide it or
  remove it
* Also need to create a way to display the route directions step
  by step
Merge pull request #13 from mknudsen01/directions-for-pin

Add route to map when click 'Get Directions'