Update stats on the home page #2434

Fixed the beginner issue #2434 Update stats on the home page,
Adjusted the parameters to make the total 0.5 million by 20 Aug 2014 as shown in the thread https://github.com/TEAMMATES/repo/issues/2434.

By Chi Cheng
![dcb](https://cloud.githubusercontent.com/assets/7929782/4216432/cb13f254-38d9-11e4-8a77-199fa01c7a7a.png)