Noticed this while reviewing #13529, but it's also in master @ 5ba77df. On macOS 10.13.6:

<img width="209" alt="schermafbeelding 2018-08-01 om 16 22 09" src="https://user-images.githubusercontent.com/10217/43527498-0f571db4-95a7-11e8-8d90-7863947a7689.png">


<img width="178" alt="schermafbeelding 2018-08-01 om 16 12 51" src="https://user-images.githubusercontent.com/10217/43526994-c9a515ec-95a5-11e8-96b8-9e2513e9aac5.png">

* `Show` in the action menu doesn't work if the app was hidden by `Command + H`, it does work when hidden through this menu
* send and receive don't unhide the window when opened for the action menu. It does navigate to the right tab. The other actions do work (sign, verify & debug window)

Clicking "Toon" (= macOS native show) does work, suggesting the GUI uses some non-native method of hiding.
{
    
    m_handler_message_box = m_node.handleMessageBox(boost::bind(ThreadSafeMessageBox, this, _1, _2, _3));
    m_handler_question = m_node.handleQuestion(boost::bind(ThreadSafeMessageBox, this, _1, _3, _4));
}
void BitcoinGUI::unsubscribeFromCoreSignals()
{
    
    m_handler_message_box->disconnect();
    m_handler_question->disconnect();
}
UnitDisplayStatusBarControl::UnitDisplayStatusBarControl(const PlatformStyle *platformStyle) :
    optionsModel(0),
    menu(0)
{
    createContextMenu();
    setToolTip(tr("Unit to show amounts in. Click to select another unit."));
    QList<BitcoinUnits::Unit> units = BitcoinUnits::availableUnits();
    int max_width = 0;
    const QFontMetrics fm(font());
    for (const BitcoinUnits::Unit unit : units)
    {
        max_width = qMax(max_width, fm.width(BitcoinUnits::longName(unit)));
    }
    setMinimumSize(max_width, 0);
    setAlignment(Qt::AlignRight | Qt::AlignVCenter);
    setStyleSheet(QString("QLabel { color : %1 }").arg(platformStyle->SingleColor().name()));
}
void UnitDisplayStatusBarControl::mousePressEvent(QMouseEvent *event)