Sum of geom in FeatureGrid

As the title says it.

Picture:
![sum_geom](https://cloud.githubusercontent.com/assets/1792111/3979110/937bf13c-2850-11e4-9df5-483342b4a251.png)

m2 => m<sup>2</sup>
Do we always use the metric system?
What about translating only the string (eg. "Total surface:"), not the whole geomSizeTpl which contains a lot of non-i18n parts?