Since initialization on first startup or during a database schema update
can take several seconds, show a splash screen. In the initial
implementation, this is just a small Clementine logo.
The benefit of instantiating the splash in the Application class rather
than in main is that it could eventually show status messages during
startup. However, this implementation does not use the
QSplashScreen::finish mechanism that would synchronize the hiding of the
splash screen with the showing of the main window.
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