SelectCommandSystemTest: update to verify selected card is visible

[Zhiyuan-Amos]

SelectCommand selects a card and scrolls to the card.

SelectCommandSystemTest does not verify that the card is visible.

Let's update SelectCommandSystemTest to verify that the person card is in the on-screen bounding box of the PersonListPanel. From taking a quick look, it seems that there's no easy way to get the (x,y) coordinates of each person card using JavaFX / TestFX. Using Flowless may help as there's API for such functionality.