Wayland: fix "grab keys" when switching from/to fullscreen

Under wayland the inhibitor class is initialized on the window() containing the remoteview widget. When switching to fullscreen, the view widget is moved to a temporary window, requiring the inhibitor class to be reinitialized on the new window. Similarly, when switching back to windowed mode, the inhibitor must be reinitialized on the main window.

This MR also removes the current implementation of RdpView::switchFullscreen(), that wrongly assumed it was its duty to activate full screen mode, while this slot is only meant to inform the view of a state change.