Fixed #8007: removed mention of admin options in models from docs/design_philosophies.txt

Models should encapsulate every aspect of an "object," following Martin

Fowler's `Active Record`_ design pattern.

This is why model-specific admin options are included in the model itself; data

related to a model should be stored *in* the model.

This is why both the data represented by a model and information about

it (its human-readable name, options like default ordering, etc.) are

defined in the model class; all the information needed to understand a

given model should be stored *in* the model.

.. _`Active Record`: http://www.martinfowler.com/eaaCatalog/activeRecord.html