Update FR translation after the Facelift series of PRs

* Translate all UIs in the Simple Style Editor into French
* Generate the .po files for `legend` and `orbisgis-core` (they were empty)

Note that I can't quite seem to figure out where to translate (Area|Line|Point) Symbolizer when it is the default legend. Maybe this isn't translatable? (Is it hidden in a .se file somewhere?) However I was able to translate it in the Advanced Style Editor.

Fixes #485.

Screenshot:

![legendpicker](https://f.cloud.github.com/assets/2470768/819341/857130b4-efaf-11e2-9760-3cddf7a177fd.png)
![translation](https://f.cloud.github.com/assets/2470768/819342/8da0aca6-efaf-11e2-9982-5d20d1646fa0.png)