Simplify return statements.

Remove redundant ‘this’.
Remove unused using directives.
Simplify LINQ chains.
Add some trait property descriptions.
Add readonly where viable.
Add fullstops to some yaml descriptions.

OpenRA.Mods.RA/Traits/Mine.cs

@@ -30,7 +30,7 @@ namespace OpenRA.Mods.RA.Traits
 
 		public Mine(ActorInitializer init, MineInfo info)
 		{
-			this.self = init.Self;
+			self = init.Self;
 			this.info = info;
 		}