Interface to deactivate gaze targets

Options:

1. Make it easy construct a gaze target that is basically "invalid" or "done", e..g

            gaze_targets::GazeTarget deletedTarget = latestGazeTarget_.value();
            deletedTarget.priority =
                gaze_targets::TargetPriority(gaze_targets::AttentionType::RandomEvent, 0.0);
            deletedTarget.keepInQueue = false;
            deletedTarget.duration = Duration::Seconds(0);
            deletedTarget.status = gaze_targets::arondto::TargetStatus::Aborted;
            srv_->viewSelectionClient.commitGazeTarget(deletedTarget);

2. Add a function to the view selection client to "deactivate" a gaze target

This is necessary e.g. when a skill is aborted.