Validators

To make it possible to change the set of validators, each node has to mountain the history of validators which were active on each block height.

Example:

"validator_sets": [
    {
      "height": 0,
      "validators": [
        {
          "public_key": "IgaBE+25uuZ32VT2oX6cvN3CuwUOvzZIZqJN+A4KrUA=",
          "power": 1
        }
      ]
    }
  ]