Change: add vcpkg.json to instruct vcpkg what dependencies we require

This works on all OSes, making it far simpler for any developer
to jump in. Just install vcpkg, run "vcpkg install" in our root,
and you have all the dependencies.

Fix: [Git] ignore any build folder you might have

Instructions now suggest using build-host, etc. It is easier to
just ignore all build* folders.

Add: introduce CMake for project management

CMake works on all our supported platforms, like MSVC, Mingw, GCC,
Clang, and many more. It allows for a single way of doing things,
so no longer we need shell scripts and vbs scripts to work on all
our supported platforms.

Additionally, CMake allows to generate project files for like MSVC,
KDevelop, etc.

This heavily reduces the lines of code we need to support multiple
platforms from a project perspective.

Addtiionally, this heavily improves our detection of libraries, etc.

(svn r27730) -Change: Split openttd.grf into openttd.grf and orig_extra.grf
openttd.grf is now always loaded and provides all extra graphics in case the (possibly outdated) baseset does not.
orig_extra.grf contains graphics specific to the original baseset only.