Add new translator for Bundesgesetzblatt (Federal Law Gazette of Germany...

...)

 * It should be freely available online. Can you access it outside from Germany (see test cases)?
 * I would like to attach the pdf directly to the entry, but it didn't suceed so far (iframe, embedded pdf, ...)
 * The icon seems sometimes not to update. It might just be a dom change and not a real new page load. What was the trick here again?
 * AFAIK the end page is not available.
 * Any other comments?
`doc.getElementById('showTextClickable').classList.contains('on')` should work nicely here. Maybe test for `doc.getElementById('showTextClickable')` first to avoid throwing errors here.