Global/General fund fixtures & css tweaks

* Add fixtures for global/general fund images
* Switch to using funds' *icon* instead of *featured_image*
* Add a CSS class for masks which will expand the mask to fill the width of its container while keeping square

Images have already been uploaded to s3 and the media directory. Looks like:

![screen shot 2014-12-22 at 12 13 38 pm](https://cloud.githubusercontent.com/assets/326918/5528968/00f57b54-89d4-11e4-88f3-964da13ee9d5.png)
![screen shot 2014-12-22 at 12 13 45 pm](https://cloud.githubusercontent.com/assets/326918/5528969/06bf6112-89d4-11e4-9fcb-1bf26350d77c.png)

mask--fill_square to keep in line with somewhat bad naming convention