Automatically add Steam wads on startup

[kenbot]

Hello! A chunky feature for your review. Addresses #279 by auto-loading Steam WADs on first init.

Of note:

• Finds Steam installation based on Windows Registry
• Finds all local Steam libraries based on the installation
• Finds all the relevant Id/Bethesda games that have usable WADs in the libraries
• If possible, loads everything it can from the new version of Ultimate Doom (ie Doom + Doom II), which includes IWADS Doom, Doom2, TNT, Plutonia, as well as PWADs Nerve, Sigil, Legacy of Rust and Master Levels.
• Otherwise loads from previously independent games Doom2 and Final Doom
• Heretic, Hexen, Strife
• Ignores failures, it doesn't matter if it can't find things.
• Adds a new dependency VDF.Gameloop to read Valve's KeyValue configuration format. This is the most popular C# library for this purpose.
• I have hooked the Steam checker into the MainForm.CheckFirstInit() method (in MainForm_Init.cs). It will auto-load from Steam, and only prompt for IWADs in the usual way if there were none found.
• It uses the existing method HandleAddGameFiles(), which does all the copying, progress bars, etc.
• Written in such a way that the untestable bit at the top of the world is very small, everything else is tested, even integration tests using a realish "Steam installation" in the testing Resources directory.
• If there is nothing new to load, it does nothing.

LMK if you'd like any changes!

[nstlaurent]

Nice! I have the doom re-release and it didn't load the main iwads for me, probably because the paths are a little different than before maybe? It found sigil, nerve, master levels, and id1.

Could be a special case since I previously only had the ultimate doom unity version from steam, then it was updated.

The path I have is: C:\Program Files (x86)\Steam\steamapps\common\Ultimate Doom\base (this has doom.wad)

From there I have the folders doom2, plutonia, and tnt.

[kenbot]

Ohhh that's interesting. I have both paths in my one, I'm not sure why. Try again now!

[nstlaurent]

Looks good, thanks!