added priority support for cluster state updates:

 * URGENT:
	* routing-table-updater
 	* shard-failed
 	* shard-started
 	* refresh-mapping

* HIGH
	* cluster_update_settings
	* reroute_after_cluster_update_settings
	* delete-index
	* update-mapping
	* remove-mapping
	* put-mapping
	* close-index
	* open-index

* NORMAL
	* _all other actions_