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.Common/Modifiers/TimedUpgradeBar.cs

@@ -0,0 +1,58 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2014 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation. For more information,
+ * see COPYING.
+ */
+#endregion
+
+using System;
+using System.Drawing;
+using System.Linq;
+using OpenRA.Traits;
+
+namespace OpenRA.Mods.Common
+{
+	[Desc("Visualizes the remaining time for an upgrade.")]
+	class TimedUpgradeBarInfo : ITraitInfo, Requires<UpgradeManagerInfo>
+	{
+		[Desc("Upgrade that this bar corresponds to")]
+		public readonly string Upgrade = null;
+
+		public readonly Color Color = Color.Red;
+
+		public object Create(ActorInitializer init) { return new TimedUpgradeBar(init.self, this); }
+	}
+
+	class TimedUpgradeBar : ISelectionBar
+	{
+		readonly TimedUpgradeBarInfo info;
+		readonly Actor self;
+		float value;
+
+		public TimedUpgradeBar(Actor self, TimedUpgradeBarInfo info)
+		{
+			this.self = self;
+			this.info = info;
+
+			self.Trait<UpgradeManager>().RegisterWatcher(info.Upgrade, Update);
+		}
+
+		public void Update(int duration, int remaining)
+		{
+			value = remaining * 1f / duration;
+		}
+
+		public float GetValue()
+		{
+			if (!self.Owner.IsAlliedWith(self.World.RenderPlayer))
+				return 0;
+
+			return value;
+		}
+
+		public Color GetColor() { return info.Color; }
+	}
+}