fix: Use isRebalanced to detect Arena cards (#5778)

* fix: Use isRebalanced to detect Arena cards

In #5759 we introduced a setting (off by default) to disable the use of
Arena cards. This was done by checking the `isOnlineOnly` property of
the card, which accidentally also disabled online *printings* of cards
that otherwise exist in paper (e.g. Vintage Masters).

This PR does the same thing but uses the `isRebalanced` property
instead, which is `true` for Arena cards only and should have been used
from the start. This setting does not impact online-only printings such
as Vintage Masters. The settings is still on by default.

* Update setting to mention Alchemy rather than Arena

oracle/src/oracleimporter.cpp

@@ -213,7 +213,7 @@ int OracleImporter::importCardsFromSet(const CardSetPtr &currentSet, const QList
 
     // mtgjson name => xml name
     static const QMap<QString, QString> setInfoProperties{
-        {"number", "num"}, {"rarity", "rarity"}, {"isOnlineOnly", "isOnlineOnly"}};
+        {"number", "num"}, {"rarity", "rarity"}, {"isOnlineOnly", "isOnlineOnly"}, {"isRebalanced", "isRebalanced"}};
 
     // mtgjson name => xml name
     static const QMap<QString, QString> identifierProperties{{"multiverseId", "muid"}, {"scryfallId", "uuid"}};