Add extraData property in ImportKeyListEntry

This allows any KeyServer to store some extra data it might need.
In the case of KeybaseKeyServer it is the username, which then can
be grabbed directly, without the hack of storing it as userId.

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/service/KeychainIntentService.java

@@ -749,8 +749,8 @@ public class KeychainIntentService extends IntentService
                 KeybaseKeyServer server = new KeybaseKeyServer();
                 for (ImportKeysListEntry entry : entries) {
                     // the keybase handle is in userId(1)
-                    String keybaseID = entry.getUserIds().get(1);
-                    byte[] downloadedKeyBytes = server.get(keybaseID).getBytes();
+                    String keybaseId = entry.getExtraData();
+                    byte[] downloadedKeyBytes = server.get(keybaseId).getBytes();
 
                     // create PGPKeyRing object based on downloaded armored key
                     PGPKeyRing downloadedKey = null;