Update 2.2.0

Hey,

Here are the main modifications brought with the version 2.2.0.

1. It is now possible to use a "guest account" to play. It is no longer necessary to create an account beforehand. In that case, your data are stored locally on your machine. However, general information such as the best scores, average errors and maps of all players are no longer visible.
2. A new game has been implemented: The table of Chemical Elements.
3. An additional mode (an easy one) has been added to the United States game.
4. + Some UI polishing.
5. + Some minor bug corrections.

Have fun!