backend: check nodes/items permission on disco#items: - move node access check workflow from getItemsData to a new checkNodeAccess method - only accessible items are returned to an entity when doing a disco#items on a node - for PEP, nodes with presence access model are not returned if entity has not presence subscription from the node owner - all nodes are returned in normal pubsub service - new NotLeafNodeError exception when an action need to be done on Leaf node and it is not the case - /!\ access it not fully checked : items access models are not handled for items id in disco#items, and whitelist nodes are returned regardless if requestor is in the white list or not. Furthermore, publisher-roster access is not handled for nodes.