Get Multiverse sets working with generate_booster

[asilano]

• [x] First, ignore the fact they change. Pull and parse on first request, then use that forever
• [ ] Later, allow for change. Pull and parse, and store with date somehow. Allow subsequent requests to use that or update or pull in parallel. Unsure exactly what. Need to think about what drafting will want.
• [x] Add support for text-dump of card if image is absent
  • [ ] ideally if image is unreachable, too
• [ ] Add support for images of multiverse cards (need to consult @alextfish for desired format and API)