Replace debug window icon with LGPL-licensed one (fixes bitcoin#1348)

Replace debug window icon with LGPL-licensed one (fixes bitcoin#1348)

* fix verification network behaviour:
- use up to 10 connections only
- save state (do not ask same nodes after restart)
- initiate on time based intervals (every 5 minutes), based not on new blocks (should keep connections alive longer)

* revert mWeAskedForVerification serialization

* send verify requests using MAX_POSE_CONNECTIONS as a step

…ner, not rank-1 mn

83e01fa [RPC][Bug] Fix masternodecurrent: return next winner, not rank-1 mn (random-zebra)

Pull request description:

  `masternodecurrent` RPC is improperly returning the masternode with rank 1 instead of the next winner.
  Closes bitcoin#1348

  ```
  > getblockcount
  2236241

  > masternodecurrent
  {
    "protocol": 70918,
    "txhash": "cfa69f018741e0960a436788391d9d2cec0f9aceed30e883a78818f7c073fba1",
    "pubkey": "DHeEycDFe9pWr3FahcnTbavy8Urb1832HU",
    "lastseen": 1583439177,
    "activeseconds": 6690804
  }

  > getmasternodewinners 0
  [
    {
      "nHeight": 2236242,
      "winner": {
        "address": "DHeEycDFe9pWr3FahcnTbavy8Urb1832HU",
        "nVotes": 10
      }
    },
    ...
  ]
  ```
  <https://explorer.pivx.link/block/9fe33eedf5f61a8e9f8d50b9007c25d1b0260f0c97f88265feda4c06dfa86725>

  Note: `GetCurrentMasterNode` returns the masternode with lower rank and it's used as winner only when no valid block payee can be found. We should probably change its name to something more meaningful (`GetLowestRankMasterNode` ?) and change the comment calling it "winner". Same goes for the comment above `CMasternode::CalculateScore` (masternodes are not even paid based on their scores, but only on the time of their last payment).

ACKs for top commit:
  furszy:
    utACK 83e01fa
  Fuzzbawls:
    ACK 83e01fa

Tree-SHA512: c6bd9b5c83900a4e269b6dd308ea083bc0d4a778ebbf1c865019d092cba9b024819d97f792d9fd34040f36034d507eda482da398a34915e9497db3bf1b70d9b3