Add CSS class "box"

Adds a CSS class that can be used to lay out boxes next to each other
Add CSS class game-box

Adds a CSS class for the div box that contains the actual game
Use jquery.equalhights plugin

Adds the jquery.equalheights plugin, to keep objects of the same class
at the same height. I hope I'm not painting myself into a corner with
this decision!
Add statistics box

Fixes #10.
Adds a box with statistics about the current game session.