Jake map kit

Changed the function for adding a new story from a button to a longpress on the screen.
Added two labels: one that tells a user how to add a story & disappears when the user tries it, and one that prompts the user to authenticate and shows up if an unauthentic user tries to add a story, and then fades away after 2 seconds.
Added a StoryPin class which is a subclass of MKPointAnnotation, which adds a story property, which allows it to store a Story object.
Filled in mapview delegate method to instantiate the ViewingStoryVC when an annotation view's callout accessory button is tapped. It sets the ViewingStoryVC's storyObject property before it instantiates.
Added calls to turn the NetworkActivityIndicator on and off, corresponding to network requests.
Added addStoryAnnotationToMapForDate function which takes in a date and a bool. If the bool is true, it only adds annotations to the map corresponding to Stories after a certain date. If the bool is false, it deletes all pins from the map and then draws annotations for all Stories.
Added a removeAllPinsButUserLocation button which removes every annotation view EXCEPT the user location. Gets called in the addStoryAnnotationToMap method.
Added outlet to centering button to map for later visual changes to the button that will be based on its contextual change of function.