[RFC] Separate external libraries and language files into VS projects

No source files were moved, the only changes were to VS solution and project files. The proposed solution structure looks like this:
![](http://puu.sh/dAaQU/3a1a167805.png)

- language project simply hold the language files. The PostBuildEvent which copies the files has been moved there.
- "libs" project holds speex, argparse and lodepng files. They are compiled to a static library (to build/libs) and linked with openrct2.dll.

Benefits:
- project - wide search will now skip language files and these libraries, which makes search results easier to navigate
- optimizations are now enabled for the libs project