Network error handling, HUD on MapView, location svcs check, etc.

-Singleton DSHTTPSessionManager instead of individual AFHTTPRequestOperationManager resources
-Use AFNetworking’s network activity indicator instead of manually turning it on/off
-User friendly station error message in release version
-HUD is displayed when station data is being loaded on mapView
-new updateLocationButton outlet to enable/disable button when location services are turned on/off
-updateLocationButton.enabled is stored in state restoration
-better stationError: handling on a state-by-state basis (generally just uses last data available)
-“Set Destination” text uses parent tintColor instead of hardcoded iOS7 blue
-check to make sure we have a valid user location before panning to it in updateLocationTapped:
-locationManager.activityType changed to CLActivityTypeFitness, should give finer location updates
-Location usage description added for when user is prompted to enable location services