Feature request: Import/export of map background palettes

[tech-ticks]

Re-coloring some of the base game's map backgrounds is very difficult and annoying because there's no option to replace palettes from an imported image without overriding chunks, which messes with animated tiles. Animated palettes can't be exported and imported at all (at least to my knowledge), so they have to be manually adjusted color by color.

It would be very handy if SkyTemple had an option to export and import palettes only without changing any other image data. The exported image just could be a PNG containing all palette data as distinct pixels (regular+animated), but maybe there's a better and more intuitive way to implement this feature. Alternatively, there could be two distinct implementations:

1. The "Chunks import" dialog could have a "Replace palettes only" toggle
2. The animated palette editor could have a button to import/export to/from an image