Adds a CountDown panel.

![countdowndemo](https://cloud.githubusercontent.com/assets/521984/2749920/89937598-c836-11e3-9650-10db7a3d4d71.png)
Takes in a the current session and computes the time until that session is done and displays that. Also for future validation reasons it has a public function to check if the game is over or not.

Edit - I've created a demo window (Show above) that counts down a session that ends on the 10th of May, 2014 at 12:02 PM. Which can be verified by comparing with wolfram alpha here: http://www.wolframalpha.com/input/?i=Time+until+10th+of+May%2C+2014+at+12%3A02+PM

Edit 2 - There are some UI improvements that we should discuss but I believe the core functionality is 100% here.