CE/map_follow_behavior

created custom "follow me" behavior to keep user centered on the map after pressing the "follow me" button.  if the user pans or zooms the map while in following mode following is cancelled.  
When a gesture recognized is added to a view, it will be retained by that view. Since we're dealing with the lifecycle of that view, and we don't have a public method to remove the behavior from the view, I think we may as well make these gesture recognizes weakly held.