LP#1268636 add expressive facet link titles

LP#1268636 add expressive facet link titles

Let the user know exactly what clicking on a facet will do.

Thanks to Dan Scott for the suggestion.

* Note that accessibility validators may dislike the repetitive titles,
  but clearly adding them provides more information (for everyone).
  Plus, as facets pile up, there's no reasonable way to differentiate
  between all titles, anyway, without title attributes becoming too
  long and unreadable.

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Dan Scott <dscott@laurentian.ca>