i18n - add mark_translated to highlight extracted strings

I didn't have much luck using Unicode as per Foreman, as table_print got confused and messed up the layout.  Strangely, it was better with its "better" multibyte option disabled, but that's probably not best.
I think it's because of this: https://github.com/theforeman/foreman/pull/851#issuecomment-23792658

When using multi-domain lookups, you end up getting an untranslated string from just one of the domains instead of it continuing to search through them until one actually returns a translated version.