Responsive design and playtesting

The game styles were updated to look fine and be playable on low screen resolutions, starting at around 640 x 360. While mobile experience is not superb, the game is still playable and looks good.

To improve mobile expectience, a full screen mode has been added.

I'll continue doing playtesting and fixing bugs found along the way (there are around 20 so far).

After two or three completions, the game should be ready to be published.