German translation 2

I created a language file from the original German version today, because there doesn't seem to be a complete one. I noticed https://github.com/IntelOrca/OpenRCT2/pull/374, but it's WIP and gets manually translated. This is not meant as a competitor, but rather as an alternative version using a different approach. The source changes are copied from that pull request, so I haven't tested them, because building on Linux doesn't seem like a lot of fun.