Allowing new styles on White Label about pages.

Lesser of two evils; adding a new attribute in the context of the about page to make sure it inherits the styles of the front pages in the LMS, rather than the courseware header. 

See https://openedx.atlassian.net/browse/ECOM-390 for more details. 

With the new header enabled, it will now appear as such:
![image](https://cloud.githubusercontent.com/assets/235752/4411120/1aea08f4-44ec-11e4-9b01-3031f8a271f3.png)

@wedaly @rlucioni