Update french translation.
Remove strings for nonexistent entry in the menu.
Add strings for new entries in the menu.

A few modifications to try to make strings easier to find/translate:
- Organize the strings in several files (header, main body, footer, etc...).
- Sort the strings by alphabetical order (by language code for each string id, keeping english first as it is the reference string).
Merge pull request #49 from glv2/locale-fr

Update french translation and organize strings.