Document click handler, only apply when needed (Button Dropdowns)

[svdvs]

In rocketbelt.button-dropdown we attach a click handler to the document so we can check if we need to close a currently open dropdown. Ideally this click handler should only be applied when when a button-dropdown element is active/open.

(Line 52)

document.addEventListener('click', function onclick(e) {
      var path = e.path;
      var pathLen = path.length;
      var shouldClose = true;