Improve game release detection

[ProbablyManuel]

The Reqtificator automatically determines the game release (Steam or GOG) by checking if the load order file is available. If both the Steam and GOG release are installed, GOG is preferred by default. This behavior can be overridden by the command line argument --game=SkyrimSE or --game=SkyrimSEGog respectively.

Unfortunately, the command line argument parsing doesn't work correctly, and therefore it's currently impossible to enforce choosing the Steam release over the GOG release. Furthermore, the command line option isn't documented outside of the changelog and less convenient for the user than an option in the GUI.

Expected Outcome

• Figure out a better way to determine the game release OR fix the command line argument parsing.