Changes ISpriteSource.Frames to be of type IReadOnlyList<ISpriteFrame>.

- Updated implementations to return a ReadOnlyList around an array (to reduce wasted memory from exposing lists or lazy enumerators around lists).
- Protect non-public ISpriteFrame classes by making them inner classes to prevent casting.
- Added an AsReadOnly extension method for lists.

OpenRA.Editor/RenderUtils.cs

@@ -1,6 +1,6 @@
 #region Copyright & License Information
 /*
- * Copyright 2007-2011 The OpenRA Developers (see AUTHORS)
+ * Copyright 2007-2014 The OpenRA Developers (see AUTHORS)
  * This file is part of OpenRA, which is free software. It is made
  * available to you under the terms of the GNU General Public License
  * as published by the Free Software Foundation. For more information,
@@ -101,7 +101,7 @@ namespace OpenRA.Editor
 				}
 
 				bitmap.UnlockBits(data);
-				return new ResourceTemplate { Bitmap = bitmap, Info = info, Value = shp.Frames.Count() - 1 };
+				return new ResourceTemplate { Bitmap = bitmap, Info = info, Value = shp.Frames.Count - 1 };
 			}
 		}
 	}