Rewrite push code to provide iOS7 style animations.
Rewrite popToViewController to provide iOS7 style animations.

This refactor updates the code to rely on popViewControllerAnimated: instead of duplicating animation work.
Rewrite replaceRightViewController code to provide either iOS7 push style or fade animations.
Add iOS7 style swipe-to-navigate-back functionality.
Document iOS7 style animations and swipe-to-navigate-back functionality.
Prefer constants to defines.
Implement iOS6+ state preservation and restoration.