Course staff can see counts

With some clarification from Dave, another attempt at [TIM-373](https://edx-wiki.atlassian.net/browse/TIM-373).  This adds the status counts directly in the XBlock, but only for course staff.

Currently, the HTML table is absolutely hideous:
![image](https://cloud.githubusercontent.com/assets/2948394/2543794/41ec9dce-b5f7-11e3-8ff9-3acaae3303a3.png)

But I'm not familiar enough with styling (particularly within the LMS) to figure out how to fix it.  @talbs is there a low-cost way to at least fix the alignment?

@ormsbee please review.