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?
use protocol-relative urls if you have to change the domain (i.e. "//www.bgbl.de...") because Chrome blocks HTTP access from HTTPS pages. If you don't specifically have to change domain, it's better to use relative URLs altogether (i.e. "/banzxaver/bgbl/start...") and let Zotero figure out the rest. This makes it a bit more reliable with proxies.