jp (xmlui): added whitelist, read_only and values_only options:

- whitelist is set on XMLUI creation, it's the same as for other frontends
- read_only is set on XMLUI display, it indicates that input are not expected
- values_only is set on XMLUI display, it indicates that only values are to be displayed (it implies read_only)

src/plugins/plugin_misc_merge_requests.py

@@ -145,6 +145,7 @@ class MergeRequests(object):
         other params are the same as for [TICKETS._get]
         @return (tuple[list[unicode], list[dict[unicode, unicode]])): tuple with
             - XMLUI of the tickets, like [TICKETS._get]
+            - node metadata
             - list of parsed request data (if extra['parse'] is set, else empty list)
         """
         if not node: