Clean up shutdown process, fix closing too early or not closing at all
08d23305: Create windows with custom unique_ptrs with deleter via makeUnique()
Windows will be deleted by QWindow::close() instead of default deletion.
884323b7: Add CaptureWindow::instances() and ViewerWindow::instance()
Use these instead of m_viewerWindow and m_captureWindows in SpectacleCore. CaptureWindow::instances() automatically grows and shrinks when capture windows are created or closed. It's too much work to ensure that m_captureWindows only contains unique_ptrs that aren't null after QWindow::close() has been called.
fc2d6251: Use QEventLoopLocker to keep Spectacle alive for notifications
Stopped using setQuitOnLastWindowClosed(false) because setting it true or false depending on the situation was too complex. Now we just create a QEventLoopLocker when we make a notification and destroy the event loop locker, which also automatically quits the application, when the notification is destroyed. To close the windows, we use SpectacleWindow::closeAll() instead of making them hidden. This automatically closes Spectacle when the QEventLoopLocker has not been created.
44e3fbd4: Don't close Spectacle until the last notification is destroyed
Some notifications can have shorter timeouts and we don't want to close Spectacle before all notifications have expired or been closed.