Refacto of Tiles handling and simplified a bit file naming for tiles/params.
By the way, fixes #297

THIS COMMIT BREAKS FILE LAYOUT AND REQUIRES MIGRATION (SEE BELLOW).

To migrate data :

cd tiles
find . '*.jpg' -exec rename 's/[^\/]*_(([0-9]{3}_){2}([0-9]{3}))/$1/' {} \;...