Put JobView inside a scroll view
Put JobView inside a scroll view

Fixes "image too tall to fit on screen" problem.

As a bonus, also allows zooming in to assist in finicky placement.

Downsides:

- We lost the "Drop Image Here" text.
  Bindings didn't want to play ball for setting hidden based on
  `jobView.image != nil`, and the scroll view allowed it to peek out from
  behind the image.
- The scrollview doesn't autosize to match the dropped image size
  the way the window used to do. That's a bit frustrating, to drop an image
  that does fit fine, but then be left to adjust the viewport manually.

[fixes #1]

jeremy-w/ImageSlicer,jeremy-w/ImageSlicer,jeremy-w/ImageSlicer