Replace keysProved and keysClaimed

These terms were somewhat confusing (and, in the case of megolm, misleading),
so replace them with explicit senderCurve25519Key and claimedEd25519Key fields.

src/crypto/algorithms/megolm.js

@@ -592,7 +592,7 @@ MegolmDecryption.prototype._decryptEvent = function(event, requestKeysOnFail) {
         );
     }
 
-    event.setClearData(payload, res.keysProved, res.keysClaimed);
+    event.setClearData(payload, res.senderKey, res.keysClaimed.ed25519);
 };
 
 MegolmDecryption.prototype._requestKeysForEvent = function(event) {