Add a List type that can contain arbitrary objects

Supports objects that the core schema may not recognize and
preserves them unmodified as runtime.Unknown

pkg/runtime/scheme.go

@@ -366,6 +366,8 @@ func (s *Scheme) DecodeInto(data []byte, obj Object) error {
 
 // Copy does a deep copy of an API object.  Useful mostly for tests.
 // TODO(dbsmith): implement directly instead of via Encode/Decode
+// TODO(claytonc): Copy cannot be used for objects which do not encode type information, such
+// as lists of runtime.Objects
 func (s *Scheme) Copy(obj Object) (Object, error) {
 	data, err := s.EncodeToVersion(obj, "")
 	if err != nil {