Reorganize actor and smudge loading.

The actor and smudge definitions are now stored
as raw MiniYamlNodes in the map.  It is now the
responsibility of the consumers to parse these
into real objects.

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

@@ -28,7 +28,7 @@ namespace OpenRA.Mods.Common.Traits
 
 		public void WorldLoaded(World world, WorldRenderer wr)
 		{
-			var spawns = world.Map.GetSpawnPoints();
+			var spawns = world.Map.SpawnPoints.Value;
 			var taken = world.LobbyInfo.Clients.Where(c => c.SpawnPoint != 0 && c.Slot != null)
 					.Select(c => spawns[c.SpawnPoint - 1]).ToList();
 			var available = spawns.Except(taken).ToList();