Working on Player Stat Screen

This pull request attempts a rough attempt at a player stat screen. Currently just a prototype foundation to show a proof of concept. Includes the following:

* Included a simple screen for overlaying text. 
* By pressing [ENTER] on the battle level, the stat screen will pop up while the button is held, displaying the name of the active player as well as their stats.
* In the future, a real, decorated stat screen will take it's place. Also, I think it would be best to trigger the stat screen by right-clicking a unit. 

Coming up as soon as possible: Actual player stat screen!