Addition of Reference class and reordering of properties within classes.

I switched a number of properties with object data types to the data type documented in the Chatter REST API, for example string or Reference. Several classes were used to represent the Reference data type, such as LikedItem, MyLike, MySubscription, and OriginalFeedItem. Classes that formerly referred to these now refer to the Reference data type. In the Chatter REST API properties are listed in alphabetic order. I reordered the properties to the same order so it's easy to compare the class and the API documentation side-by-side.