Update french translation.

Here is an updated french translation with some fixes to typos or errors I saw in the context of the app.

Please merge :)
@vreixo is right, some of these strings are still commented out.

@kalon33 You'll need to submit a new PR that removes the leading `<!--` and trailing `-->` from the lines that still have it.  For example, this line should be `<string name="map_markers_warning_live_udpates">Mises à jour temps réel</string>`.