Middle click on item opens it in a new tab.

In order to stick to the old RIL extension behavior, and to do so before the dreaded FF57 lands, this is an attempt to have the items behave like good old 'a' links, especially with the middle click.

Note: as a side effect, this disables middle click scrolling in the popup (given that general.autoScroll is set to true in about:config); a lead to avoid this side effect might consist on changing items’ inline elements from 'span' to 'a' nodes.