Game simu now handle touch events.

- Added a spatial hash in the screen classes.
- Added an optionnal AvatarIndex to Avatars so that they can be stored
in the spatial index.
- Added the possibility to start a NewtSurface without decoration to
prevent a bug (or strange feature) in Jogl.
- Added a setXYGrid() method in LinesMesh to allow quickly draw grids.
- Added a debug grid in the MenuScreen to allow precisely know where we
draw.
- Added a system of Size specification to easily define the avatar size
based on comparaison with other elements or from sizes stored in the
resource libraries.
- Added a Sprite class that represent avatars made of one or more
images.