Merge the two Dutch translations

Also includes many new strings. Dutch is nearing completion now.

I restored most of my own translations. Some explanation:
- Lift chain hill and cable lift are two different things. The first is the well-known method to pull cars up, the second is a unique part of the Giga Coaster that pulls the train up at 24 km/h, using, you guessed it, a cable. The Goliath in the Six Flags Holland scenario uses it (the same goes for the real-life version!).
- I kept 'Autorondrit' as the translation for 'Car ride', since it seems to be a more 'official' term, if you like, than 'Rit in een karretje' (as it was translated in RCT1)
- I kept 'Tutorial', since it's mostly used untranslated (in Dutch RCT forums for example, most of which are sadly long gone).
- I kept 'Smalspoorweg' as the translation for 'Miniature Railway', but I would be fine with 'Miniatuurspoorweg' if most native Dutch speakers find it better.

(There may be some other things. If you wonder why I translated something in a particular way, feel free to ask it.)