General uncontroversial cleanup:

- Made private methods static where possible (runtime can elide checking the object for null).
- Declared attribute classes as sealed (allows reflection on attributes to complete faster).
- Moved some static cctor's into field initializers (static cctor's are slower than static field initializers).
- Made classes static if they contained only static methods (can't create instances of useless objects).
- Use inferable Exts.Lazy and not new Lazy<T>().
- Added required STAThread attribute to CrashDialog.
- Removed unused parameters in private methods.
- Added Serializable attribute to exceptions.
- Added parameter name in calls to ArgumentNullException.
- Use of as operator instead of is + cast.
- Changed (x as Foo).Bar anti-pattern into ((Foo)x).Bar. Results in sensible cast exceptions on error rather than null dereferences.
- Removed unused method in NullShader.

OpenRA.Game/FileSystem/MixFile.cs

@@ -73,7 +73,7 @@ namespace OpenRA.FileSystem
 			);
 		}
 
-		List<PackageEntry> ParseHeader(Stream s, long offset, out long headerEnd)
+		static List<PackageEntry> ParseHeader(Stream s, long offset, out long headerEnd)
 		{
 			s.Seek(offset, SeekOrigin.Begin);
 			var numFiles = s.ReadUInt16();
@@ -87,7 +87,7 @@ namespace OpenRA.FileSystem
 			return items;
 		}
 
-		MemoryStream DecryptHeader(Stream s, long offset, out long headerEnd)
+		static MemoryStream DecryptHeader(Stream s, long offset, out long headerEnd)
 		{
 			s.Seek(offset, SeekOrigin.Begin);
 
@@ -121,7 +121,7 @@ namespace OpenRA.FileSystem
 			return ms;
 		}
 
-		uint[] ReadBlocks(Stream s, long offset, int count)
+		static uint[] ReadBlocks(Stream s, long offset, int count)
 		{
 			s.Seek(offset, SeekOrigin.Begin);