If the popover's title contains no text, hide it via JS. Previously was
done via CSS's `:empty` property, but that doesn't work in IE8, so JS
it is.

/cc @fat becaue I probably did this wrong <3

add show/shown hide/hidden events to dropdown + update dropdown links for testing + catch a few missed namespace things

change dropdown strategy to use an overlay - fixes mobile click anywhere + allows for firefox middle click