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 
I think I was wrong: I thought you could `bind-attr` to the inverse of a property, but it seems you can't. For reference https://github.com/emberjs/ember.js/issues/2714.