Add non-Arena sets about draftmancer HOT 1 CLOSED

Obviously opening the app to non-Arena users would be cool.
Here's what's preventing me to start working on that:

• Arena IDs are used as unique ID for cards internally, we'd have to change to another ID set. This is fixable, and probably desirable even if we don't introduce non-Arena cards (helps supporting incoming sets earlier, handle some duplicate within the Arena DB...), but it's still a scary change.
• DB Size. Right now all card data is just loaded on startup. We'd have to load additional "vintage data" on demand (probably too large), or re-think how to supply card data entirely (full card objects in every message instead of just an ID?).
• I expect a lot of corner cases with older cards, but I may be worrying for nothing.
• It's just a lot more to test, and I'm already missing a lot of regressions all the time :D

from draftmancer.