Change modal to use API instead of special page, refactor

* Call schema.GettingStartedNavbarNoArticle (name to be changed) from
  the modal JS here (since it won't be called by the server)
* Handle article selection failures more gracefully.  Before we we show users
  the task choice page.  We now simply remove a button, or don't show the dialog.
* Change doFixPages to use direct article URL, rather than go through
  the special page.
* Refactor how dialog and buttons are created, partly since dialog and
  buttons depend on whether we can get a suggested URI
* Get rid of dialog API and just pass the close method, which is always called
  before the button's dedicated click handler.
* Remove obsolete TODOs.
* Move code out of $(document).ready that doesn't need to be there.
* Remove unused width parameter.

Change-Id: Ic03250321e23946be92d8f373bd6112639ea51c9