Adds zenity as part of winetricks.

[danieljohnson2]

I totally didn't mean to just jam this in! This should be a PR. Is this too hacky to live?

This clones and builds zenity and copies it into the winetricks package. There's a corresponding PR for the Lutris client that will use this if present.

And since this (default) zenity does not use webkit2 or gstreamer, it works on the latest Ubuntu. Or so I hope.