Some typo in the book

[Chu-Te-Ethan-Chen]

Hi, it great to read your django-admin-cookbook. It helps me a lot. While reading the book, I might find some typo in the text.

1. sublass -> subclass
   docs/add_model_twice.rst
2. AllEntiryAdmin -> AllEntityAdmin
   docs/database_view.rst
   I wish it could be helpful to you.
   Thank you very much.