plugins xep-0060, xep-0277: added methods to serialise getItems result (before bridge transmission): serItemsData is used for normal callbacks, and serItemsDataD for callbacks which return deferred. These methods simplifly the code by making the re-use of getItems more easy.

# TODO: remove this when RSM and MAM are in wokkel
import wokkel
from sat.tmp.wokkel import delay as tmp_delay, pubsub as tmp_pubsub, rsm as tmp_rsm, mam as tmp_mam
wokkel.delay = tmp_delay
wokkel.pubsub = tmp_pubsub
wokkel.rsm = tmp_rsm
wokkel.mam = tmp_mam