added validations for Trip address and lat/longs with spec test
added messages to presence validations for trip spec
fixed validations bug, all lat and longs now save
implemented condiational on geocode validation to run unless coordinates are already set
Refactored trip creation workflow
* Created a CoordinatesRetriever class which takes a trip as an argument and returns an array of coordinates from the trip addresses
* Re-wrote TripsController#create to retrieve the coordinates for the trip instance
* Removed Trip before_validation callback which calls the geocoder
* Removed methods irrelevant to the Trip model linked to the before_validation callback