[Liznoo] Removed FBSD_HEADERS.
[Liznoo] Fixed path to FreeBSD backend.
[Util] Added ExecuteFuture().
[Liznoo] Implemented CanChangeState() for PMUtils backend.
[Liznoo] Implemented CanChangeState() for UPower backend.
[Liznoo] PowerActions::Platform::CanChangeState().
[Liznoo] Check if it's possible to change state before changing.