Monitor (Master)

Provided changes from 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

Added ability to request monitor statistics via elliptics protocol.