Support tabbing through controls in modals, popovers, and selects

I rebased the work that @thangdinh did, as he will be unable to work on this for a while. Not very familiar with the code, so hoping that someone else is.

@cyril-sf @azirbel @Dylnuge @jpriceAddepar 
```
focusElement = hasFocus[0]
if focusElement.className.indexOf("close") > -1 
  # if we have more than two tabbable objects, we do not want to tab to
  # while if we do not have any choice, the close button is chosen
  if hasFocus.length > 1
    focusElement = hasFocus[1]
focusElement.focus()
@set 'currentFocus', focusElement
```