[Shotwell] Prevent showing trashed images

[John Tyree]

When sifting through a new import, I typically look at the photos one at a
time, in large view and press delete as I see fit. I notice, however, that
'deleted' images stay in the buffer such that pressing the back arrow will
revisit them. When flipping back and forth between many photos, it can be
confusing as to whether or not a photo has already been deleted. Pressing
`esc` to return to the many-photos view correctly hides the trashed image
and upon zooming back in, the image is no longer accessible. Is this a bug
or pebkac?

Also, is there a hotkey to ALWAYS go to the next image or previous image?
Say I zoom in to look at something, and then want to move on to the next
image. Left and right do not do that unless the entire image is visible,
otherwise they pan around. ctrl, alt, shift modifiers have no effect as far
as I can tell. Neither do PgUp/PgDn (which would be perfect for this, I'd
say).

-John