Updates Norwegian Bokmål translation

Changes and updates to the Norwegian Bokmål translations based on the current pot files. 

I assumed the pot files were up to date, but I've since seen #363. So I'm not sure whether we want to merge this now, or wait until the new pots have be generated. I will probably look over the translations again once that happens, but to reduce the amount of conflicts it might be better to merge this first. (Though up to you, of course)