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.
{
    
    if(event->mimeData()->hasUrls())
        event->acceptProposedAction();
}
void BitcoinGUI::dropEvent(QDropEvent *event)
{
    if(event->mimeData()->hasUrls())
    {
        for (const QUrl &uri : event->mimeData()->urls())
        {
            Q_EMIT receivedURI(uri.toString());
        }
    }
    event->acceptProposedAction();
}
bool BitcoinGUI::eventFilter(QObject *object, QEvent *event)