Add badge font size

Hi, 

I've made this little tiny fix allowing the user to change the badge font size. Seems to produce exactly the same result as before when not using the new property.
 
Looks like this with the sample project when the new setting is not used:

![Screen Shot 2012-12-13 at 2 41 23 PM](https://f.cloud.github.com/assets/271047/10638/d7029af6-452a-11e2-8861-242cc291589c.png)

When setting :

    	cell.badgeTextFontSize = 15.0;

It looks like this :
![Screen Shot 2012-12-13 at 2 41 46 PM](https://f.cloud.github.com/assets/271047/10640/dbca4cb4-452a-11e2-9cc1-713d6cfb5db9.png)

An even  better solution would be to center the label vertically since it is slightly too low with fonts higher than 11 (which is the default size)