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/Crates/Crate.cs

@@ -121,7 +121,7 @@ namespace OpenRA.Mods.Common.Traits
 
 				// Make sure that the actor can collect this crate type
 				// Crate can only be crushed if it is not in the air.
-				return self.IsAtGroundLevel() && mi.Crushes.Contains(info.CrushClass);
+				return self.IsAtGroundLevel() && mi.LocomotorInfo.Crushes.Contains(info.CrushClass);
 			});
 
 			// Destroy the crate if none of the units in the cell are valid collectors