Adding Filterable Featured Image Size

We should add a default image size of `large` instead of `full` for the featured image.

![why_your_company_needs_a_wootrip](https://f.cloud.github.com/assets/1065372/1313891/320ed1cc-3264-11e3-976c-1210e201a681.png)

FYI this is untested since my internet connection is garbage at the moment.