Main program entry point rework (configuration, arguments)

[ForNeVeR]

• 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).