Add option to patch `My Games` save location to not collide with retail

[mrexodia]

Currently I use a custom client that has the 2 occurrences of My Games patched to Sapphire on disk. I can easily implement this as an in-memory patch behind a setting. Let me know if you would accept such a PR, otherwise I won't bother.

[NotAdam]

~~I don't remember if its in the older client, but I'm pretty sure that there's a command line arg you can pass to move the whole directory somewhere else - I'll have a look when I'm home~~

not in the 3.3 client - patch like this would be good to have