import "books.model" and styles for admin page

[aseds]

importing "mysite.books.model" prompts an error in last chapter we commented the 'django.contrib.staticfiles' which makes the admin page not having CSS

[suhailvs]

@ASEDS thanks for your pull request. i have update mysite.books.models to books.models in my repository https://github.com/suhailvs/djangobook.com/.

about django.contrib.staticfiles, it is better to sever the static files in some other way(apache or nginx) in production, so i didn't updated those.

I am planning to maintain the repo, because this book is wonderful. feel free to fork it and send me pull requests.