Folder for dhewm3-exclusive fixes

[justtoask]

Describe the feature you want
Essentially the game would have an additional folder called anything, for example dhewm and the source port would treat it like an additional game folder, with files like base and d3xp to load after the main files.

• base
• d3xp
• redux
• dhewm
• • base
• • d3xp
• • redux

What problem does it solve?
It would fix the issue of having to manually install and uninstall fixes for mods which have adjustments for the source port if you wanted to play the game without it for whatever reason, for example the doom 3 redux dhewm3 compatibility patch replaces the game00.pk4 file with one without a dll file, so currently you just have to switch between the files depending how you want to play.