message: Add testnet checkpoint
diff: @@ -379,12 +379,13 @@ public:
  checkpointData = {
  {
  {42, uint256S("37cf752dfcda2c1c3f1a1a3ff3b7ef47c40d0e06f8c16e058a3b04cfa1566acb")},
  + {1600, uint256S("66959ef58a234711c64c5f609f6b44a597b02ccfedea6557e1ee08fe792fb747")},
  }
  };
  chainTxData = ChainTxData{
  // Data from rpc: getchaintxstats 4096 0000000000000037a8cd3e06cd5edbfe9dd1dbcc5dacab279376ef7cfc2b4c75
  - /* nTime */ 1543868766,
  + /* nTime */ 1544074723,
  /* nTxCount */ 19438708,
  /* dTxRate */ 0.626
  };
  