backend, pgsql storage: better items/notification handling, various fixes: - replaced const.VAL_AMODEL_ROSTER by const.VAL_AMODEL_PUBLISHER_ROSTER to follow change in pgsql schema - implemented whitelist access model - fixed bad access check during items retrieval (access was checked on recipient instead of requestor/sender) - getItemsData and notification filtering now use inline callbacks: this make these complexe workflows far mor easy to read, and clarity is imperative in these security critical sections. - publisher-roster access model now need to have only one owner, else it will fail. The idea is to use this model only when owner=publisher, else there is ambiguity on the roster to use to check access - replaced getNodeOwner by node.getOwners, as a node can have several owners - notifications filtering has been fixed in a similar way - psql: simplified withPEP method, pep_table argument is actually not needed - removed error.NotInRoster: error.Forbidden is used instead - notifications now notify all the owners, not only the first one