Images: add support to download set/rarity svg icons from scryfall or remove it at all?


Set's icons (rarity icons) used in very limited placed by xmage:
* card viewer (if icon available);
* m15 render mode (if icon available);
* ~~popup text mode (if icon available)~~ (not used any more);

Current version uses gatherer source for set's icons download. It's low quality and outdated (without sets from last few years);

Scryfall can be used as high quality source of that icons (like mana icons). It's require to do:
* implement set's svg icons download from scryfall (in symbols download pipeline, simple scryfall api from set's endpoint);
* implement set's icons generations by color (scryfall icons are black and white but xmage require rarity colors);

Set's icons are useless now, but in the future it may be used by some potential app's features (decks, drafts or collection related features for better GUI or information).

I prefer to delete set icons at all and replace it by rarity chars like C,U,R,M,S (deck editor already use same logic). It will simplify code support and improve user experience in download tasks (current version generate too much errors and other logs while symbols download).

But it open for any potential ideas about that icons usage.