Add cross-platform MonoGame-based emulator surface

[nilllzz]

• Adds a new project that uses MonoGame (DesktopGL) to allow for a cross-platform compatible emulator surface.
• Parameters of that project can be configured using the Config.json file.
• Games are loaded from the Games/ directory in the execution direction.
• Removes WinForms references from the main lib project to allow building on non-Windows platforms
• Disables WinSound on non-Windows platforms for now since it can only be built on Windows. Alternative sound options have to be explored.

CoreBoy running on Ubuntu 19.04 using MonoGame:

CoreBoy running on Windows 10 1909 using MonoGame:

Currently only keyboard input is supported, but can easily be extended to work with controllers with the MonoGame.Input api.

[davidwhitney]

This is amazing, I'll have a play and try get these in over the weekend. Thanks for the effort! 🖤