Row image

So here's this... lol. Passing tests included.

Basically, it adds the ability to set `{image: "my_image"}` or `{image: UIImage.someImage}` on any cell and it will set the cell's `imageView.image` property. Images should be 40 points x 40 points.

Let me know how you want to document this (and where) before you merge this and I'll take care of it in this branch.

Cheers! :beers: