Add labellable representation when inherited from Lims::Api::LabellableResource
user
```ruby
require 'lims-api/core_resource'

module Lims::Api
  class LabellableResource < CoreResource

    module Encoder
      # TODO: when using ruby 2.0, the following code can be replaced
      # using "prepend" as it includes the module below the class in 
      # the inheritance hierarchy. We can then call super() to access
      # the core_resource to_hash_stream method.
      module Representation
        # Include the default representation from CoreResource in 
        # the LabellableResource::Encoder::Representation module.
        include CoreResource::Encoder::Representation

        module AliasToHashStream
          def self.included(klass)
            klass.class_eval do
              alias :original_to_hash_stream :to_hash_stream
            end
          end
        end

        module Labellable
          def to_hash_stream(h)
            original_to_hash_stream(h)
            object.labellable_to_stream(h, @mime_type)
          end
        end

        module NoLabellable
          def to_hash_stream(h)
            original_to_hash_stream(h)
          end
        end
      end
    end

    def self.encoder_class_map
      Encoders.mash { |k| [k::ContentType, k] }
    end

    Encoders = [
      class JsonEncoder
        include CoreResource::Encoder
        include Lims::Api::JsonEncoder
        include Encoder
        include Representation::AliasToHashStream
        include Representation::Labellable
      end
    ]
  end
end
```
assistant