Implement Health Status view, fixes #306

Initial PR.

To follow up:
- list localizers with https://github.com/pascalchevrel/list_localizers (per repo/per year, and globally for the locale) And maybe globally for all locales
- Improve view performances (cache)
- Fix getStatsPaneDP test (currently disabled)
- Shall we remove code for http://transvision.mozfr.org/showrepos/ or both views should coexist?
- Last commit is most of the times from L10n Drivers, even on Desktop
- Shall we merge in the UI some of the components on Desktop?
- Prettify UI
getColumns returns only the keys, we need keys + values here. So maybe I should do this:
    public static function getColumnsId()
    {
        return array_keys(self->$columns);
    }
    public static function getColumnsName()
    {
        return array_values(self->$columns);
    }

I guess $columns can be private, yep