Add listbox gui element

[kumpu]

This already exists in the game but can't be used in mods, which is a shame. Please add it, nothing more to say here

[kumpu]

If anyone is interested, I was able to achieve the desired result by abusing buttons.
I still think this should be added.

[Mooncat]

For the image, you probably just need 3 pixels with 3 different colors.

If listbox element is implemented, it will be great if it optionally supports shift and ctrl operations like the ones in my Creative Mode:

The current implementation is far from generic, so it is not easy to use it for another mod.

[kumpu]

Oh that's kinda neat. You should make it generic and get it included into stdlib!