Dutch translation improvements

DO NOT MERGE YET! STILL WIP!

I'm looking at the Dutch translations and see if I can fix or/and improve some translations. I will look further today at this, so till I say it, do not merge it yet. In the mean time the other Dutch translators (for example @Gymnasiast ) can look at the changes I have made so far and can descide if it's a good change or not. Just want to let you know I'm working on it, so we don't do dubble work :) 
@Gymnasiast Aha, het was dus de slechte Nederlandse vertaling in RCT2 die mij op het verkeerde been zette... Dus zullen we het volgende doen?: 
-Prijs voor....(bijv. het veiligste park, de beste rustige attracties etc.)
-Park met de beste/slechtste prijs/kwaliteitsverhouding.