Added yellow fade effect to FAQ items

We link to FAQ items from a couple of pages on Gratipay. Because of the two column layout, it's hard for a user to know what exactly we've linked to. This PR adds a transparent yellow background to the item. It fades out within 3s of page load. 

[Yellow fade effect](https://signalvnoise.com/archives/000558.php)

Screenshot: 
![highlight](https://cloud.githubusercontent.com/assets/3893573/4347740/909dab38-4167-11e4-90e9-51bc359fcfe6.png)