Fix #202 - Update and review French translations.

Just a note: the label for the first instruction of a walk leg seems to be "Turn depart", which in French does not make sense: "Tourner départ" (and I think in English neither incidentally). It may be the wrong label combination used for the first walk instruction (seems to be [step_by_step_turn] + [dir_relative_depart]), I leave people with more experience on the code to check / correct this.