Some optimization + balancing the XP gain

Hi again

Well there is some interesting change, I now keep the total acceleration in the watch, it permit to have better stat and be closer to the movement of the player for the XP.

I updated the icon of the watchface to look like VaultBoy.

The player can heal the vault boy when charging the watch.
The check for limb crippled/healed is now every 20 mins (or more like every 20 sample of accelerations, meaning it only take into account when the watchface is activated and not just the time it is).

Corrected a bug when the watchface was giving XP when starting it. It shouldn't do that.