[ENH] Add upload images to other places in ThemeEditor

Rather than having to access the “Upload Images” feature from (only) the ••• menu of Theme Editor, could we also get an “Upload Images” button wherever else a User might have the impulse to change backgrounds?

Such as:
• Edit Theme > Global TileStyle > Background Image dialogue;
• Edit Tile > TileStyle > (proposed) Background Image dialogue;

It’s just a tad cumbersome to have to back out of nested dialogues to add images, then return for the sake of selecting an image.

P.S. I still say it’d be nice to have “Swap Background Image” as a new type of Tile (Style) Override. Will go make sure this got listed under [ENH] section for voting on.