plugin PubSub Schema: schema helper methods: 3 new methods are introduced by this patch: - psSchemaUIGet to get XMLUI from node schema - psItemsFormGet to get items as XMLUI when we know they are data forms - psItemFormSend to set item from values when we know it's a node with schema. For this method, schema can be specified, and if it is not it will be retrieved from node (which imply an additional XMPP request)