Allow creating an image occlusion from the clipboard

[dae]

Previously mentioned on #2631

[abdnh]

Instead of adding a "Select image from clipboard" button, what about making the existing button ask the user whether they want to use the image in the clipboard if any is detected?

[dae]

Hmm. I would think it might be a bit simpler to have two different buttons - that way the user doesn't need to deal with a pop-up when an image happens to be on the clipboard but they want to select an image, and when they want to use the clipboard, they don't need a separate confirmation step. WDYT?

[abdnh]

I think I agree. The two-button approach is also probably better for discoverability.

[glutanimate]

IOE used a single-button approach with no confirmation, but I don't think we need to be bound to its UX here and would agree that a two-button solution is the more intuitive and discoverable option.