Update french translation

  - Add 5 missing translations
  - Fix some grammar mistakes
  - Try to unify some translations
    * "QR-code" everywhere instead of "code QR" in some places
    * "indexation" instead of "indexage"

I used Poedit 1.6.4 under Windows. It automatically wrap long lines, sorry about that, I didn't succeed to disable this in settings. It also delete trailing spaces.