Made fetch low priority

app/src/main/java/eu/faircode/email/DaoOperation.java

@@ -34,6 +34,7 @@ public interface DaoOperation {
             " WHEN operation.name = '" + EntityOperation.HEADERS + "' THEN -2" +
             " WHEN operation.name = '" + EntityOperation.SYNC + "' THEN" +
             "  CASE WHEN folder.account IS NULL THEN -1 ELSE 1 END" + // outbox
+            " WHEN operation.name = '" + EntityOperation.FETCH + "' THEN 2" +
             " ELSE 0" +
             " END";