Add a per-player handicap option to the lobby.

Handicaps reduce unit health, firepower, and build speed.

OpenRA.Mods.Common/Traits/Multipliers/HandicapDamageMultiplier.cs

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+#region Copyright & License Information
+/*
+ * Copyright 2007-2020 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, either version 3 of
+ * the License, or (at your option) any later version. For more
+ * information, see COPYING.
+ */
+#endregion
+
+using OpenRA.Traits;
+
+namespace OpenRA.Mods.Common.Traits
+{
+	[Desc("Modifies the damage applied to this actor based on the owner's handicap.")]
+	public class HandicapDamageMultiplierInfo : TraitInfo
+	{
+		public override object Create(ActorInitializer init) { return new HandicapDamageMultiplier(init.Self); }
+	}
+
+	public class HandicapDamageMultiplier : IDamageModifier
+	{
+		readonly Actor self;
+
+		public HandicapDamageMultiplier(Actor self)
+		{
+			this.self = self;
+		}
+
+		int IDamageModifier.GetDamageModifier(Actor attacker, Damage damage)
+		{
+			// Equivalent to the health handicap from C&C3:
+			//  5% handicap = 95% health = 105% damage
+			// 50% handicap = 50% health = 200% damage
+			// 95% handicap = 5% health = 2000% damage
+			return 10000 / (100 - self.Owner.Handicap);
+		}
+	}
+}