Don't force prefixed-translation of administration section dragged from XWiki.ConfigurableClass objects

The current behavior is to prefix the section name with "admin." to build a message key, and display this message key translated.

If the translation key does not exists, we should rather display the section name directly, instead of admin.sectionName. There are some use cases where you don't want to bring translations with your application. Especially considered there is no way to add translation automatically with your app, yet.