Tidy up AwfulPostsViewTopBar (né AwfulPageTopBar).
Add more responsibility to posts view, which is no longer a scroll view.

Rewrote the top bar stuff so the posts view moves it around, approximating the
old approach that required a scrollInset.top without requiring a scroll view
that can handle scrollInset.top.
Formatting and sorting.
Always show posts view top bar when VoiceOver is enabled.