Monitor (LTS)

Changed name 'io_queue' to 'io'
Added monitor to export for using it with elliptics-client
Added status of io pool: blocked or not
Added statistics about output queue: current size and total count
Removed monitor dependency from node
Added statistics provider for io pools and output queues
Removed rwlock from monitor
Used timestamp of statistics request instead of elapsed time from previous request
Removed clearing commands history after each statistics request