Added french translation

[louiswolfers]

Didn't see #87 and I feel like I lost my time, but mine removes some random capital letters.

Nevermind :( still adds the french translation tho.

[Ajimi]

@louiswolfers I think you forget some string resources for example :

    <string name="activate_signal">Activer le Signal</string>
    <string name="verify_signal">Verifier le Signal</string>
    <string name="enter_verification">Entrez le code de vérification que vous avez reçu à l'étape Enregistrement du signal</string>
    <string name="cancel">Annuler</string>
    <string name="register_title">Enregistrer avec Signal</string>
    <string name="register_signal_desc">Enregistrer un nouveau numéro de téléphone (+12125551212) avec Signal pour envoyer des notifications sécurisées. N'UTILISEZ PAS VOTRE NUMÉRO DE SIGNAL EXISTANT / PRIMAIRE.</string>
    <string name="phone_hint">+12125551212</string>

    <string name="menu_licenses">Licences...</string>
    <string name="sensor_light">Lumière ambiante</string>
    <string name="sensor_accel">Mouvement (Accelerometer)</string>
    <string name="sensor_camera">Mouvement (Camera)</string>
    <string name="sensor_sound">Microphone</string>
    <string name="sensor_power">Alimentation USB</string>
    <string name="sensor_unknown">Inconnu</string>

Take a look #103

[louiswolfers]

Fixed it. @n8fr8, could you merge?