Added straightforward hover behavior for all units. Give a unit a nonzero Altitude: in its Mobile: block and the WithShadow: trait to make it hover.

OpenRA.Mods.RA/Move/Move.cs

@@ -95,6 +95,14 @@ namespace OpenRA.Mods.RA.Move
 		public override Activity Tick( Actor self )
 		{
 			var mobile = self.Trait<Mobile>();
+			var info = self.Info.Traits.Get<MobileInfo>();
+
+			if (mobile.Altitude != info.Altitude)
+			{
+				if (mobile.Altitude < info.Altitude)
+					++mobile.Altitude;
+				return this;
+			}
 
 			if (destination == mobile.toCell)
 				return NextActivity;