message: [Qt] properly copy IPv6 externalip MN info
  IPv6 addresses use `:` rather than `.` characters in their notation,
  so needed to change the way `externalip` was being copied here.
diff: @@ -240,7 +240,7 @@ void MasterNodesWidget::onInfoMNClicked(){
  ))) {
  // export data
  QString exportedMN = "masternode=1\n"
  - "externalip=" + address.split(":")[0] + "\n" +
  + "externalip=" + address.left(address.lastIndexOf(":")) + "\n" +
  "masternodeaddr=" + address + + "\n" +
  "masternodeprivkey=" + index.sibling(index.row(), MNModel::PRIV_KEY).data(Qt::DisplayRole).toString() + "\n";
  GUIUtil::setClipboard(exportedMN);
  