The DesktopView replaces the default ConfigView for itself with a
specialised ContainmentConfigView. It's only loaded by the desktop, and
is more of a Desktop-ConfigView than generic containment.
The system tray applet doesn't show it's own config, but instead shows a
config of its internal system tray containment by overriding the
configure action.
This causes the desktop view to mistakenly shows it's specialised
desktop config view when the system tray is configured.
This patch adds an explicit check on the containment type.