Add show sprite button to scene tagger list

[Flashy78]

Resolves #3534

Adds an image icon to each scene in the tagger view that displays the sprite file in a lightbox. The icon doesn't not show up if there is no file for the scene.

Suggestions on a better UI than shown in #3534 are welcome.

[WithoutPants]

The alternative I think would be similar to the duplicate scene checker tool. I'd move the icon to be overlapping the bottom right corner of the thumbnail, and have the sprite image show on hover. Showing the sprite image in a lightbox seems like too much to me, but I'm not totally against it.

[DogmaDragon]

The alternative I think would be similar to the duplicate scene checker tool. I'd move the icon to be overlapping the bottom right corner of the thumbnail, and have the sprite image show on hover.

Something like this would be my preference. Maybe it's just me not being used to lightbox or me being used to how the dupe checker displays it.

[Flashy78]

I moved the icon to overlap the top left of the thumbnail, it was much easier than caclulating where it needs to be if the thumbnail is portrait or landscape, and also because there can often be a useful watermark in the bottom right that is nice not to cover when tagging.

I found being able to zoom into the image very useful sometimes, so the lightbox worked best for me.
I also didn't want to be instrusive to existing users by having something randomly popping up and taking over their screen as they moved their mouse around.