UI: disable old list code
UI: introduce ListModel::cell() accessor
RCORE: provide Update request structures
UI: use UpdateRequest structures for ListModel & ListRelay notifications
Merge branch 'list-update-request'

* list-update-request:
  UI: use UpdateRequest structures for ListModel & ListRelay notifications
  RCORE: provide Update request structures
  UI: introduce ListModel::cell() accessor
  UI: disable old list code