Create menu graphics

[Bigorneau]

We need a clean and simple menu design

As the game is (for now) an infinite deathmatch, we thought of having the settings on top of the game view, as an overlay.
This should be quite easy to implement as a Playground state.

However, it would be much faster to use pure HTML (forms, etc) for this.

[Bigorneau]

Might use work done for #9 for a player inputs mapping menu/overlay