Update NBClient to popover presentation-style
Update NBClient to popover presentation-style

Now checks size classes instead of UI idiom. Using the same view
controller also reduces code.

> 'UIPopoverController' is deprecated: first deprecated in iOS 9.0 -
  UIPopoverController is deprecated. Popovers are now implemented as
  UIViewController presentations. Use a modal presentation style of
  UIModalPresentationPopover and UIPopoverPresentationController.

nationbuilder/nationbuilder-ios