private-browsing module updates

This branch includes bug fixes for:

* [Bug 777823](https://bugzilla.mozilla.org/show_bug.cgi?id=777823): private-browsing module's isActive property should return true only if any window is in PB mode
* [Bug 777830](https://bugzilla.mozilla.org/show_bug.cgi?id=777830): Update private-browsing module events for per-window PB
* [Bug 822863](https://bugzilla.mozilla.org/show_bug.cgi?id=822863): Add 'private' option to windows.open
* [Bug 825471](https://bugzilla.mozilla.org/show_bug.cgi?id=825471): Jetpack broken due to the changes to the old private browsing service.