Added IDisabledTrait & rewrote upgrade code using a level-based approach.

Upgradeable traits are notified whenever an upgrade of their declared types are granted or revoked.  The traits maintain their own internal level counter, which is then used to enable or disable the trait functionality.  A trait can register for multiple upgrade types which then all affect the internal level counter.

	IDisabledTrait for identifying (and filtering) disabled traits
	UpgradableTrait provides an abstract base for traits to support upgrade levels
	Added IDisabledTrait support to GlobalButtonOrderGenerator

	Includes rework by pchote with alterations.

OpenRA.Mods.RA/Armament.cs

@@ -12,6 +12,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using OpenRA.GameRules;
+using OpenRA.Mods.Common;
 using OpenRA.Primitives;
 using OpenRA.Traits;
 
@@ -24,7 +25,7 @@ namespace OpenRA.Mods.RA
 	}
 
 	[Desc("Allows you to attach weapons to the unit (use @IdentifierSuffix for > 1)")]
-	public class ArmamentInfo : ITraitInfo, Requires<AttackBaseInfo>
+	public class ArmamentInfo : UpgradableTraitInfo, ITraitInfo, Requires<AttackBaseInfo>
 	{
 		public readonly string Name = "primary";
 
@@ -53,18 +54,11 @@ namespace OpenRA.Mods.RA
 		[Desc("Use multiple muzzle images if non-zero")]
 		public readonly int MuzzleSplitFacings = 0;
 
-		[Desc("Enable only if this upgrade is enabled.")]
-		public readonly string RequiresUpgrade = null;
-
-		[Desc("Disable if this upgrade is enabled.")]
-		public readonly string RestrictedByUpgrade = null;
-
 		public object Create(ActorInitializer init) { return new Armament(init.self, this); }
 	}
 
-	public class Armament : ITick, IExplodeModifier, IUpgradable
+	public class Armament : UpgradableTrait<ArmamentInfo>, ITick, IExplodeModifier
 	{
-		public readonly ArmamentInfo Info;
 		public readonly WeaponInfo Weapon;
 		public readonly Barrel[] Barrels;
 
@@ -78,13 +72,10 @@ namespace OpenRA.Mods.RA
 		public int FireDelay { get; private set; }
 		public int Burst { get; private set; }
 
-		bool requiresUpgrade;
-		bool restrictedByUpgrade;
-
 		public Armament(Actor self, ArmamentInfo info)
+			: base(info)
 		{
 			this.self = self;
-			Info = info;
 
 			// We can't resolve these until runtime
 			Turret = Exts.Lazy(() => self.TraitsImplementing<Turreted>().FirstOrDefault(t => t.Name == info.Turret));
@@ -108,27 +99,11 @@ namespace OpenRA.Mods.RA
 				barrels.Add(new Barrel { Offset = WVec.Zero, Yaw = WAngle.Zero });
 
 			Barrels = barrels.ToArray();
-
-			// Disable if an upgrade is required
-			requiresUpgrade = info.RequiresUpgrade != null;
-		}
-
-		public bool AcceptsUpgrade(string type)
-		{
-			return type == Info.RequiresUpgrade || type == Info.RestrictedByUpgrade;
-		}
-
-		public void UpgradeAvailable(Actor self, string type, bool available)
-		{
-			if (type == Info.RequiresUpgrade)
-				requiresUpgrade = !available;
-			else if (type == Info.RestrictedByUpgrade)
-				restrictedByUpgrade = available;
 		}
 
 		public void Tick(Actor self)
 		{
-			if (requiresUpgrade || restrictedByUpgrade)
+			if (IsTraitDisabled)
 				return;
 
 			if (FireDelay > 0)
@@ -226,7 +201,7 @@ namespace OpenRA.Mods.RA
 			return barrel;
 		}
 
-		public bool IsReloading { get { return FireDelay > 0 || requiresUpgrade || restrictedByUpgrade; } }
+		public bool IsReloading { get { return FireDelay > 0 || IsTraitDisabled; } }
 		public bool ShouldExplode(Actor self) { return !IsReloading; }
 
 		public WVec MuzzleOffset(Actor self, Barrel b)