Bump up overlay z-index

Creatives need a z-index of `1052` to go on top of the header. So the overlay then appears on top, need to increase its z-index 

### Before

![screen shot 2014-06-26 at 17 13 16](https://cloud.githubusercontent.com/assets/74132/3401155/06dc732e-fd4d-11e3-95f1-151006829264.jpeg)

### After

![screen shot 2014-06-26 at 17 12 17](https://cloud.githubusercontent.com/assets/74132/3401157/0abc55ae-fd4d-11e3-831a-17018b578508.jpeg)