placeViewImage: Remove GdkPixbuf

Use textures instead.

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I'm getting a warning in the console:

GtkStack 0x5617031bb460 reports a minimum width of 256, but minimum width for height of 1048576 is 350. Expect overlapping widgets.

But it also appears on main. I'm not sure how to get the behavior we want without getting that warning.

Fixes #584 (closed)