Revert "Revert "Show the modal overlay as soon as openWindow is called""

Reapplying ca6a16f613e186bec05a481e36dff5eb9f70e0e8.

Changes:
* Incorporate f1abca8e82 (parent selector for hiding)
* Show windows after setup, rather than after ready,
  otherwise windows are not yet visible when their
  ready process runs, which breaks focusing elements
  inside windows from the ready process

This reverts commit 234cd9f9c51b0467d2933b5a78a65881f96215bc.

Change-Id: If3ea64421c2a85fcb57a967ae10514a1ad448570
Merge "Revert "Revert "Show the modal overlay as soon as openWindow is called"""