applets/kickoff: close on session/power action
The power and session actions currently do not explicitly close kickoff like starting an application does. In most cases this has no consequence as kickoff will be closed by the session/power action itself or its consequences. There are some, though, that do not necessarily do so; one of them is sleep if the computer is configured to not lock the screen on waking (otherwise locking would close kickoff).
This change makes the power/session buttons behave like regular entries and close the popup when activated. The user can still prevent this by pinning kickoff.