Fix French translation

[eochu]

Hello all,

I read in the following discussion that there is already a French translation team:
#16744

However, I think the following Device Statuses have a bad French translation (my suggestions in «»):

Failed -> Échoué (« En panne »)
Decommissioning -> Démantèlement (« En cours de désactivation », or « En cours d'arrêt »)
Staged -> Mis en scène (am not sure of the meaning of Staged status but Mis en scène is clearly not suitable :) )

What does the French translation team think about these changes?

[jeremystretch]

Please submit any proposed translation corrections on Transifex.