Reader second pass: detail view redesign, refactoring, and improvement

For #602 in absence of a new design for the detail view, I reused the same design we're using for the Reader list view. This reuse is both in the UI and in code. We have a new `ReaderPostView` that can be reused/embedded elsewhere in the future, e.g. as a way to view your own posts. This view can toggle between showing a summary, and showing the full content of the post. It works on iPhone and iPad, so this also improves the detail view on iPad.

Along the way I did a bunch of refactoring to remove redundancies, move handlers out of views and into controllers, and general cleanup. The following additional issues will be resolved as a result: #416, #645, #704.

Worth highlighting is a trick to preload images before they're visible. The approach (which @tomwitkin learned from another developer) is to use a `UITableView` that is taller than the screen. The cost is additional maintenance of that modified height. We'll need to watch for bugs resulting from this trick, e.g. I had to fix the reblog form positioning.

![readerdetail](https://f.cloud.github.com/assets/515035/1676601/44258ec2-5d1c-11e3-9bfa-7d4cdb41723d.png)

Video:
https://cloudup.com/cOvyJ9eWoou