Clean up lots of win32 crustiness

[tari]

This builds on top of #74 to remove a lot of old crusty patterns that mostly relate to targeting Windows as a primary platform. Using CMake, vcpkg and C++17 features:

• all uses of raw win32 APIs are removed in favor of standard C++
• the COM interface is removed (nobody seems to care about it and making it work with cmake seems hard)
• app signing on Windows doesn't depend on random prebuilt .lib files anymore (GMP will be automatically built from source if needed)
• dependency on OpenSSL is removed in favor of shipping a public-domain implementation of MD5