Consider deprecating magic props

[jfroelich]

I am now more comfortable with incurring deserialization cost and performing explicit deserialization at the model layer. I have also introduced, long after beginning to use magic, explicit entity classes like Entry and Feed. Therefore, there is less of a need to use magic. Instead, I can use simple instanceof type checks in the various sanity checks. Therefore, I think I would like to eventually deprecate the use of magic fields.

[jfroelich]

I moved away from the object-oriented approach because it paid serialization cost for relatively little benefit. Therefore magic props are still useful.