message: qt: Make BitcoinGUI aware of runtime palette change
  This change fixes the GUI when changing appearance on macOS.
diff: @@ -1250,7 +1250,17 @@ void BitcoinGUI::message(const QString& title, QString message, unsigned int sty
  void BitcoinGUI::changeEvent(QEvent *e)
  {
  +#ifdef Q_OS_MACOS
  + if (e->type() == QEvent::PaletteChange) {
  + overviewAction->setIcon(platformStyle->SingleColorIcon(QStringLiteral(":/icons/overview")));
  + sendCoinsAction->setIcon(platformStyle->SingleColorIcon(QStringLiteral(":/icons/send")));
  + receiveCoinsAction->setIcon(platformStyle->SingleColorIcon(QStringLiteral(":/icons/receiving_addresses")));
  + historyAction->setIcon(platformStyle->SingleColorIcon(QStringLiteral(":/icons/history")));
  + }
  +#endif
  +
  QMainWindow::changeEvent(e);
  +
  #ifndef Q_OS_MAC // Ignored on Mac
  if(e->type() == QEvent::WindowStateChange)
  {
  