ehnc Featured projects section

Based on newest designs:

https://18f.slack.com/files/ericronne/F02TL5AM4/peacecorps-donationlanding-11-04-14.png

Created a background image class with a centered one for this use case
and a bordered class with white modifier.

Other changes:
- Added left right paddings to all headings, need to fix up.
- Added no bottom margin class for text. Useful for many headings

output:
![screen shot 2014-11-04 at 4 09 20 pm](https://cloud.githubusercontent.com/assets/1701077/4910518/b6e9e1da-6480-11e4-8205-868f3625b67f.png)

![screen shot 2014-11-04 at 4 10 11 pm](https://cloud.githubusercontent.com/assets/1701077/4910519/bbe8246c-6480-11e4-8647-d37ab5279700.png)

![screen shot 2014-11-04 at 4 10 35 pm](https://cloud.githubusercontent.com/assets/1701077/4910520/bf171418-6480-11e4-8096-a962fae89151.png)