Added a bunch of TraitLocationAttributes

Also moved a few traits to their proper subfolders.

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

@@ -17,6 +17,7 @@ namespace OpenRA.Mods.Common.Traits
 {
 	[Desc("Sets a custom terrain type for cells that are obscured by back-facing cliffs.",
 		"This trait replicates the default CliffBackImpassability=2 behaviour from the TS/RA2 rules.ini.")]
+	[TraitLocation(SystemActors.World | SystemActors.EditorWorld)]
 	class CliffBackImpassabilityLayerInfo : TraitInfo
 	{
 		public readonly string TerrainType = "Impassable";