added image gallery support in project posts

Altered public/css/screen.css and _layouts/project.html to include image gallery support in projects. Screenshot of results attached and usage in README.md under "images"

![screen shot 2014-11-02 at 8 37 14 pm](https://cloud.githubusercontent.com/assets/5509591/4877931/dd749452-62fb-11e4-9167-4336f6486196.png)