Main program entry point rework (configuration, arguments)

- Drop all the old resource extraction code from the `Program.fs`.
- Leave the bmp extractors, though: they are still useful occasionally.
- Game data path should no longer be passed via the command line.
- Instead, an optional path to the configuration file should be accepted via an environment variable.
- The configuration file should have a parameter with the game data directory, defaulting to the `LocalAppData` (or `.cache` or whatever it's on macOS).
- We could also use a game-provided configuration file with defaults (i.e. distribute the default configuration with the game); just make sure to properly support the platform-dependent cached data path there, i.e. by introducing a `%CACHE%` placeholder.
- After we did this, remove the `launchSettings.json` from `.gitignore` (it should no longer be required to pass any non-shareable parameters there).