Fix for showcase image as first image

Fixing the fullscreen button placement when a showcase image is used as the first element of an article.
Also removed the use of gallery classes in the article pages.

Before:
![screen shot 2014-11-21 at 10 48 05](https://cloud.githubusercontent.com/assets/2236852/5141300/e6bfefc4-716b-11e4-8250-c6d2cda47615.png)

After:
![screen shot 2014-11-21 at 10 48 32](https://cloud.githubusercontent.com/assets/2236852/5141310/0521a9d0-716c-11e4-9058-5d97f15299c2.png)