Merge image gradient fixed height with hero unit.

 Enhance the way gradients are used

![image](https://cloud.githubusercontent.com/assets/2095625/3538075/2232d266-082a-11e4-89d8-b5514aca98eb.png)

![image](https://cloud.githubusercontent.com/assets/2095625/3538080/2ac3f68a-082a-11e4-9228-7f7e3b460932.png)