Completed + reviewed Dutch locale

Unfortunately i forgot to pull changes (again) and i ended up with some merge conflicts. The only commit that matters is the last one. Strangely enough the other two are other commits i made, intertwined with code changes i didn't make (at the moment i only do translations). They're probably from the (late) pull i did. I don't know if these will cause any issues, but github says it can merge them in automatically.