* Keep the GUI alive when closing a game
Make HLE.Switch init when starting a game and dispose it when closing
the GlScreen.
This also make HLE in charge of disposing the audio and gpu backend.
* Address Ac_k's comments
* Make sure to dispose the Discord module and use GTK quit method
Also update Discord Precense when closing a game.
* Make sure to dispose MainWindow
* Address gdk's comments
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