Delete unused font_size setting from Settings.plist.

(Though I imagine it'll soon make a return.)
Move AwfulPostViewModel to Posts folder.
Tidy up AwfulLoadingView.

* Delete unused AwfulLoadingViewType enum.
* -retheme defaults to no-op.
* "Loading" label defaults to Dynamic Type font.
* Adopt newer coding style.
Tidy up UINavigationItem+TwoLineTitle.

* Delete redundant property declaration.
* Document -titleLabel property.