Sixth chapter version 1

How to build cliffs and jumpers (exercice completed).
Changed a pro-error dialog

Instead of ask if we want to quit the game, we must ask if we want to
continue it. This way, the player have just to say "yes" two times to
continue with a saved game, not with a "yes and no" answers where the
player can be wrong and quit the game even if he wouldn't.
Merge tag 'chapter5.1' into HEAD

Fifth chapter, version 2
Merge tag 'chapter6.1'

Sixth chapter, version 2
Seventh chapter version 1

Starting a new nomenclature for files and translating them, adding a
cave to train with teleporters and adding little houses map for exercices.