New Reader list design

This is the new design implemented for #485: layout, typography, padding, buttons, and colors. It includes many aesthetic changes as well as an overall code cleanup and refactoring. It only changes the list view, not the detail view.

There are some known shortcomings:
* The comments button does nothing yet. This will change once comments are unified in another pull request.
* You can browse to a tag, but this experience isn't great yet; improvements are outside of this scope.
* The experience of scrolling remains imperfect (ideally images would almost always load off-screen, but this doesn't happen); also outside of this scope.
* The iPad experience could be much more beautiful and deserves its own design in the future.

Screenshot (iPhone):
![newreader-iphone](https://f.cloud.github.com/assets/515035/1566728/c5184406-5093-11e3-80f3-c6d6faea52ea.png)


Screenshot (iPad):
![newreader-ipad](https://f.cloud.github.com/assets/515035/1566690/1c6dcff6-5093-11e3-809f-fe010156e16d.png)

Video:
https://cloudup.com/cNo8p0iztTA