Split Locomotor trait from Mobile

Add GrantConditionOn*Layer traits

This allows to
- drop some booleans from Locomotor
- drop a good part of the subterranean- and jumpjet-specific code/hacks from Mobile
- grant more than 1 condition per layer type (via multiple traits)
- easily add more traits of this kind for other layers

OpenRA.Mods.Common/Traits/World/SubterraneanLocomotor.cs

@@ -0,0 +1,40 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2018 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 System.Collections.Generic;
+using OpenRA.Traits;
+
+namespace OpenRA.Mods.Common.Traits
+{
+	[Desc("Used by Mobile. Required for subterranean actors. Attach these to the world actor. You can have multiple variants by adding @suffixes.")]
+	public class SubterraneanLocomotorInfo : LocomotorInfo
+	{
+		[Desc("Pathfinding cost for submerging or reemerging.")]
+		public readonly int SubterraneanTransitionCost = 0;
+
+		[Desc("The terrain types that this actor can transition on. Leave empty to allow any.")]
+		public readonly HashSet<string> SubterraneanTransitionTerrainTypes = new HashSet<string>();
+
+		[Desc("Can this actor transition on slopes?")]
+		public readonly bool SubterraneanTransitionOnRamps = false;
+
+		[Desc("Depth at which the subterranian condition is applied.")]
+		public readonly WDist SubterraneanTransitionDepth = new WDist(-1024);
+
+		public override object Create(ActorInitializer init) { return new SubterraneanLocomotor(init.Self, this); }
+	}
+
+	public class SubterraneanLocomotor : Locomotor
+	{
+		public SubterraneanLocomotor(Actor self, SubterraneanLocomotorInfo info)
+			: base(self, info) { }
+	}
+}