Verified Receipt page layout fixes

Reorg of the receipt page header to match rest of the flow; removed cart-list class from receipt page wrapper.

@dianakhuang and @jbau can you confirm that this change will not affect the edX verified certificate and Stanford shopping cart? 

@talbs can you review my FED work?
Just as an FYI, we're switching to 'enroll' instead of 'register' to describe enrollment in a course.