add blocks per second to logging

[DenisCarriere]

{
  "last_block_num": 30404,
  "last_timestamp": "2015-08-04T03:19:42.000Z",
  "blocks": 11154,
  "rows": 22310,
  "blocksPerSecond": 301,
  "totalBytesRead": 285284924,
  "totalBytesWritten": 0,
  "runningJobs": 0
}