The footer image (footer.png) is displayed near the barcode.
The allotted space is 286 x 15 points.
Images are scaled (preserving aspect ratio) to fill this allotted space.
Images with a different aspect ratio than their allotted space are cropped
after being scaled.
The logo image (logo.png) is displayed in the top left corner of the pass,
next to the logo text. The allotted space is 160 x 50 points;
in most cases it should be narrower.
PassKit displays the first supported barcode in this array.
Note that the PKBarcodeFormatQR, PKBarcodeFormatPDF417,
PKBarcodeFormatAztec, and PKBarcodeFormatCode128 formats are all valid
on iOS 9 and later; therefore, they do not need fallbacks.
