Various improvements

Major changes:
- Added image support
- Removed holding a reference to the indexPath
- Fixed slippery scrolling

OK, I think I remember why I had to attach the index path to the damn cell: there are points where `indexPathForCell` returns nil. When it does that, you get weird behavior (this screenshot is running on your fork with no changes on my end): 

![ios simulator screen shot jun 30 2014 9 34 03 pm](https://cloud.githubusercontent.com/assets/1976498/3438417/2d435d56-00c8-11e4-9e2e-7d6d84d486c6.png)

It's a good thought, but it's got some holes in practice, unfortunately.