Update to .NET Core, new project scaffold, and update path handling

[enovales]

This is a major update:

• the project files were updated using the new dotnet templates
• updated to use SQLite PCL, to allow for cross-platform compatibility
• updated tests to use Expecto
• the project is updated to build against .NET Standard 2.0 (net471 on Windows). On Linux and Mac, self-contained deployments are produced.
• some Windows-specific functionality (PInvoke extensions, and support for Star Wars: Galactic Battlegrounds Saga) was split into libraries and a plugin that are only built on Windows
• updated to new F# project scaffold