Add user config to override `com.mojang` path

[ink0rr]

This is mainly for working on a non-Windows platform, an example case would be when using mcpelauncher on macOS, where the default com.mojang path is $HOME/Library/Application Support/mcpelauncher/games/com.mojang.

It's technically possible to just use the exact mode for it, but that means I have to setup a different export profile for every OS in every project, which is not ideal.