More fixes, translated remaining string

As indicated by AaronVanGeffen.

I quickly walked trough the entire file, fixing some translations, including a few for consistency, and a few to prevent overflowing. Also translated what _seemed_ like the only remaining untranslated string! (Not counting strings that are currently untranslatable.) In other words, it means dutch.txt is as complete as it can currently get.

@AaronVanGeffen: could you take a look as well and tell if you can find any errors?
I chose this shorter translation to prevent overflowing of the buttons. (Overflowing happens when the text is longer than the button itself.) Considerations like that are behind many more strings, but sometimes it's hard to see why I chose a particular translation without knowing the context.

I generally don't look at the original Dutch translation of RCT2, since it was horrendous. RCT1's translation was better, but still contained some strange errors. For my translation, I picked many translations from RCT1, some from the internet (especially for theme park jargon, such as ride names and track parts) and some from common sense.

Currently the Dutch translation is complete. This will change when more translatable strings are added to the game. The quality of my Dutch is high, in my opinion. It does mean that I set quite high quality standards for the translation of OpenRCT2, since I have seen too many bad translations in other projects. 

Of course, I make errors as well, and suggestions are welcome. It's also why I think a review of translations, like you're doing now, is a good idea. So no, I wouldn't mind at all :).