Always move VoiceOver focus to the current view

Without this, VoiceOver user has to touch-explore to get to the left and right
views. And when top view is restored, they might end up in "nowhere" with
VoiceOver. So post notification to VoiceOver that screen has changed so that
it can reread it and focus the right element.
Merge pull request #1 from dusek/accessibility.iOctocat

Always move VoiceOver focus to the current view