Bug 885404 - Reintroduce hiding non-current pages in homescreen.

This puts back in place a change that was first introduced in 2d4ce6b3fb7f75d140cefeded599022a186db596.
Bug 885404 - Rework the a11y page controls in the homescreen.

There is a much more direct way of doing this now, thanks to IndieUI. The previous range widget and keyboard listeners were a horrible idea :P
Bug 885404 - Use click listener so icons could be activated with the a11y layer.

Update:
 - Added click listener for doc items as well.
Bug 885404 - Add click listener test to unit tests. Remove page navbar aria value asserts.
Make scrollrequest listener conditional on screen reader.