Issue #174: show lang files stats (number of files/strings/words) on listpages view

Also changed the wording of "Translate" to "Translations" and "Show" to be more explicit.
This should be something like
```
            $reference_locale = Project::getReferenceLocale($current_website);
            $source_lang_file = LangManager::loadSource($current_website, $reference_locale, $current_filename);
```
The idea is that views shouldn't know how sources.php is structured. I would also rename ```source_lang_file``` to ```reference_data´´´ for consistency with other views.