Downloads multiple pages

And added size label (quality) as a command-line option.
now that I look properly at it (sorry), I think it would be a nicer flow if we put all the fetching logic inside the `while` loop. So just init `photos = []`, start with `pagenum = 1`, and then do the `getPhotos()` inside the loop. Make sense?

I can also land this and tweak it myself.