Update French translations

[Antoine Besnier]

Hi, 
I wanted to update the French translations, as they have not been corrected for 
a long time, and some sections have not been translated at all.Would the issue 
GUACAMOLE-1159 ( 
https://issues.apache.org/jira/browse/GUACAMOLE-1159?jql=project%20%3D%20GUACAMOLE%20AND%20text%20~%20french),
 which is closed, be suitable if I submit a PR, or would I have to open a new 
issue?
Thanks in advance, Antoine