Rework mod enumeration / caching.

- Replaced ModMetadata.AllMods with Game.Mods.
- Store / reference mod Manifest instead of ModMetadata.
- Removes engine dependency on ModContent class.

OpenRA.Game/FileSystem/FileSystem.cs

@@ -13,7 +13,6 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
-using System.Reflection;
 using OpenRA.Primitives;
 
 namespace OpenRA.FileSystem
@@ -34,9 +33,15 @@ namespace OpenRA.FileSystem
 
 		// Mod packages that should not be disposed
 		readonly List<IReadOnlyPackage> modPackages = new List<IReadOnlyPackage>();
+		readonly IReadOnlyDictionary<string, Manifest> installedMods;
 
 		Cache<string, List<IReadOnlyPackage>> fileIndex = new Cache<string, List<IReadOnlyPackage>>(_ => new List<IReadOnlyPackage>());
 
+		public FileSystem(IReadOnlyDictionary<string, Manifest> installedMods)
+		{
+			this.installedMods = installedMods;
+		}
+
 		public IReadOnlyPackage OpenPackage(string filename)
 		{
 			if (filename.EndsWith(".mix", StringComparison.InvariantCultureIgnoreCase))
@@ -108,9 +113,9 @@ namespace OpenRA.FileSystem
 				{
 					name = name.Substring(1);
 
-					ModMetadata mod;
-					if (!ModMetadata.AllMods.TryGetValue(name, out mod))
-						throw new InvalidOperationException("Could not load mod '{0}'. Available mods: {1}".F(name, ModMetadata.AllMods.Keys.JoinWith(", ")));
+					Manifest mod;
+					if (!installedMods.TryGetValue(name, out mod))
+						throw new InvalidOperationException("Could not load mod '{0}'. Available mods: {1}".F(name, installedMods.Keys.JoinWith(", ")));
 
 					package = mod.Package;
 					modPackages.Add(package);