Image & URL Fields on Wireframe & Comp Forms

* Updates the wireframe and comp form partials with a layout for specifying image "or" url in a 2-up field configuration.
* **Caution:** using a css/webkit only solution for styling the file input. Since this is a project for internal use only, and we're all on Chrome & Safari anyway, it _should_ be okay. If @joshkorr deems otherwise, I will swap out with a cross-browser JS solution.
* Custom select inputs: css only solution which works in webkit and firefox.

![image](https://f.cloud.github.com/assets/283397/2448718/bb1708ba-aea9-11e3-9c72-1ad7bfc4ada3.png)