Visually draw attention to in-view references when they are selected

[iislucas]

Sometimes I've clicked number reference, but the test being referred to is already in view, so nothing visually happens. At first I thought it was a bug, and I clicked more frantically and then looked at JS console. If the highlighted section visually pulsed or something, then it would have drawn my visual attention appropriately to the highlight that is already in view.

This is less of an issue for highlights not in view since there is a nice scroll highlight into view already.

[ellenjiang7]

Thank you for the suggestion! We've incorporated a pulse animation on scroll.