Add support for UniversalUE4Unlocker

[frostworx]

copy/paste of the (wip & offline) stl UniversalUE4Unlocker wiki:

UniversalUE4Unlocker

NOT COMMITTED YET

UniversalUE4Unlocker is a mighty tool, which (re-)enables the dev console in UE4 games
and provides a nice configuration gui for changing/manipulation UE4 internal settings.
As the gui requires dotnet, automatic enabling is not implemented in stl (yet)

The tool ships a UniversalUE4Unlocker.dll though, which can be automatically injected per game via stl using IGCSInjector
by simply enabling UUUSEIGCS in Game Menu
(this automatically enables USEIGCS)

As UniversalUE4Unlocker doesn't allow direct downloads, the file needs to be manually downloaded from the project page
and extracted to $STLDLDIR/uuu (usually ~/.config/stl/downloads/uuu/)

When a game ist started with enabled UUUSEIGCS and the UniversalUE4Unlocker.dll is missing, a requester is opened where the project page
can be copy/pasted into a browser and the destination directory $STLDLDIR/uuu can be opened via xdg-open.
When done, click OK and the regular function will continue using the files.

By using the UniversalUE4Unlocker in combination with IGCSInjector
it is possible to inject VR compatibility for several regular UE4 games!

[frostworx]

Unfortunately UUU requires at least the .Net function
Windows.Foundation.UniversalApiContract
which is not shipped with dotnet 4.7.2 from Steamworks Shared.
Means the UUU gui also requires a full dotnet 4.7.2 install, which will lead to the same problems like the Vortex installation has (see winetricks wiki)

I hope installing winetricks into proton wineprefixes won't become a problem generally

[frostworx]

Added in release v6.13