French translation files

Here are the french translation files, both the .po file and the .mo file.

Note that the .po file is not exactly made from the .pot file you submitted.

I use poedit to do the translation and it does not like (in fact refused to update my language file) when two base strings are the same, in this case, the plugin URL and the author URL.
So I've removed the second one.

I also added gettext keyword (via poedit) so that I could properly input plurals.