translate some strings to french

[mquinson]

That's very far from being done, but I prefer submitting it right away just in case I don't find the time to finish this before the next french speaking guys stumbles on polymorphable.

Thanks for that project, Mt

[stefanbeller]

I guess you need to also uncomment french in mods/polymorphable/engine/languages.txt so it can be selected from within the game.