Q3A install wizard

I added an install wizard for installing Q3A, it does three things:

1. Locate an existing Q3A installation
2. Install from CD
3. Install from Steam.

It also downloads the latest Q3A patch data if needed. In hindsight, this should be separate from the install wizard. I'll move it later. The URL is hardcoded to use a local web server for now. I used the official Linux Q3A patch, since it's easy to extract (tar.gz after you skip some junk) and you don't need to worry about repackaging id's installer causing legal issues.

Plenty of things are quite rough so far, but it's a decent starting point.