Vomnibar: fix some issues about focus/blur events
Vomnibar: fix some issues about focus/blur events

* old usages of focusByCode_ and firstShowing_ seem to be just typos
* wait 50ms before `document.hasFocus()` gets ready

gdh1995/vimium-plus,gdh1995/vimium-plus,gdh1995/vimium-plus