Allow the user to make their install portable.

I love OpenRCT2 but it would be even better if it could be made fully portable by it being able to put all files into the main OpenRCT2/Launcher directory.

Normally this is done by adding "--user-data-path=.data" in the .exe launch options of OpenRCT but I think it would be great if this could be an option in the launcher, to make it truly portable.

Start at the launch configuration or entry point that builds the OpenRCT2 executable command. Check how the launcher could expose an option to use --user-data-path=.data and keep files under the main OpenRCT2/Launcher directory. Done means the option produces a fully portable installation.

Written by the indexing model from the issue text.