Modernize AwfulBrowserViewController.

- Use the built-in toolbar instead of our old custom one.
- Use AFNetworkActivityIndicatorManager instead of just setting the indicator
  visibility directly.
- Fixes #256.
Delete unused resource "action.png"
Move as many images as possible to asset catalog.

- Efficient packing format on iOS 7.
- Organize everything in one place.
- Keep @2x versions with @1x versions.
Delete unused images.